Recycling system for a waste processing plant

ABSTRACT

A recycling system for a waste converting apparatus collects residues from a post-processing means and re-introduces the residues into the apparatus such that the residues are exposed to the high temperature zone thereof.

TECHNICAL FIELD

The present invention relates to a plant or apparatus for the conversionof waste, including the processing, treatment or disposal of waste. Inparticular, the present invention is directed to an improved arrangementfor treating residues, including fly ash and the like generated by sucha plant, and for reducing the levels of dangerous emissions and thevolume of residue which are eventually output by the plant.

BACKGROUND

The processing of waste including municipal waste, medical waste, toxicand radioactive waste by means of plasma-torch based waste processingplants is well known. Referring to FIG. 1, a typical prior artplasma-based processing plant (1) comprises a processing chamber (10)typically in the form of a vertical shaft, in which typically solid, andalso mixed (i.e., generally, solid plus liquid and/or semiliquid), waste(20) is introduced at the upper end thereof via a waste inlet meanscomprising an air lock arrangement (30). One or a plurality of plasmatorches (40) at the lower end of the chamber (10) heats the column (35)of waste in the chamber (10), converting the waste into gases that arechanneled off via outlet (50), and a liquid material (38) (typicallymolten metals and/or slag) which is periodically or continuouslycollected at the lower end of the chamber (10) via reservoir (60).Oxidising gases or fluids, such as air, oxygen or steam (70) may beprovided at the lower end of the chamber (10) to convert char residuescomprising carbon, produced in the processing of organic waste, intouseful product gases such as CO and H₂, for example. A similararrangement for dealing with solid waste is described in U.S. Pat. No.5,143,000, the contents of which are incorporated herein by referencethereto.

During operation of such a plant (1), products of the waste gasificationare generated, including gases, liquid droplets and solid particles,which are removed from the chamber (10) by the outflow of product gasestherefrom via outlet (50).

The product gases include gases such as for example hydrocarbons withgeneral formula CnHm, and also CO, H₂, N₂, CO₂, H₂O, HC1, H₂S, NH₃, HFand other gases.

The liquid droplets may contain a variety of chemical compounds, and thephysical form of the liquid may range from a tar-like substance to alight water soluble distillate.

The solid products may consist of small particles of waste (which arecarried out by gas via outlet (50)) and of small particles of solidcomponents which were formed as vapor in the lower (hotter) part ofreactor or chamber (10), and then were condensed in the upper part ofthe chamber (10). These products may also include dioxins produced fromthe raw material in the waste. These solid particles which are carriedout from the chamber (10) are typically known as “fly ash”. The greaterthe speed of the product gases leaving the chamber (10), the greater theamount of fly ash that is removed from the chamber (10). This fly ashgenerally comprises organic and inorganic compounds. Organic compoundsmay include, for example, components of paper, textile and othermaterials, which in turn may also comprise some proportion of inorganicmaterials too. For example, inorganic matter may constitute more than20% of paper used in some paper products, the inorganic matteroriginating from the mineral fillers and coating pigments, including forexample calcium carbonate, china clay and metal oxides, used to providecolour inks in the printing process. The inorganic compounds may alsoinclude different salts and metals, other than just oxides thereof, andmay form part of raw waste material and/or may be formed duringreactions at the lower part of chamber (10).

Typically, the product gases including the liquid and solid productsentrained therewith are channeled off to a suitable post-processingmeans (2) comprised in the plant (1) and operatively connected to thechamber (10) via outlet (50), illustrated in FIGS. 2(a), 2(b), 3(a) and3(b). The actual form of the post-processing means (2) will generallydepend on the specific use of the plant (1) and its size/capacity.

For example, as illustrated in FIG. 2(a), in some large-scale plants(1), the post-processing means (2) may comprise an afterburner (3) andan energy generating system (4), followed by a gas cleaning system (5)and stack (6). The energy generating system (4) is adapted to produce(typically electrical) energy, which may be used to run the plant (1)and/or exported. As illustrated in FIG. 2(b), in smaller-scale plants(1), such as for example those used for the treatment of medical orother hazardous waste, may not provide sufficient product gases tojustify an energy generating system, which is therefore replaced with acombustion products cooling system (9).

In the plants illustrated in FIG. 2(a) and FIG. 2(b), the gasificationproducts generated in, and channeled off from, the chamber (10) aredirected into the afterburner (3) wherein all organic materials (ingaseous, liquid or solid form) are combusted, forming CO₂, H₂O, N₂,SO_(x), HCl, HF, P₄O₁₀, NO_(x) and other combustion products, andwherein the inorganic materials form oxides and salts. Depending on thecomposition of the original waste, and if temperature in the afterburner(3) is not high enough and/or residence time of gases therein is small,dioxins may be formed. In order to eliminate dioxins, the combustiontemperature needs to be higher than 850° C. (or higher than 1200° C. ifthe amount of chlorine in the waste is greater than about 1% by mass),and residence time in the afterburner (3) also needs to exceed 2seconds. Under these minimal conditions, dioxins (that may exist in thegas products introduced into the afterburner (3)) will be oxidized, andthus destroyed.

While dioxins may exists in the waste materials before processing, inprior art apparatuses the major proportion of dioxins is formed duringcombustion of materials, including chlorine-containing organicmaterials, especially if the combustion temperature is low and theresidence time in the afterburner is also low. Further, fly ash alsotends to contain some metal compounds, especially copper-containingcompounds which act as catalysts helping to form dioxins which areadsorbed in the fly ash, leading to high levels of toxicity in the flyash formed with prior art apparatuses. In any case, even if thecombustion temperature and residence time is sufficiently high toprevent the formation of dioxins in the afterburner, enough dioxins maystill be formed during the cooling of combustion products in the boiler.This is particularly so if some of the organic materials in the wastewere not fully combusted in the afterburner. To prevent this productionof dioxins, it is necessary to have a high combustion temperature and toquench the products of combustion.

Alternatively, and as illustrated in FIG. 3(a) and FIG. 3(b), thepost-processing means (2) may comprise a gas cleaning system (5′), forremoving from the product gases leaving the chamber (10) toxic andcorrosive components, such as for example HCl, HF, H₂S and so on, andalso including Cl, S, F and others, and also oils, tars, dust, carriedwith the product gases. The gas cleaning system (5′) is connected to awaste water treatment system (7), which also cools and cleans the waterbefore recycling. The clean fuel gas leaving the gas cleaning system(5′), typically comprising CO, H₂, N₂, CO₂, CH₄ is channeled to asuitable energy generating system (4) operatively connected to a stack(6), as illustrated in FIG. 3(a). In the energy generating system (4),the fuel gases are combusted in a gas turbine arrangement, which isoperatively connected to an electric generator, and typically also to anair compressor. Hot combustion products (at a temperature of about 450°C. to 550° C.) from the gas turbine are directed to a boiler where steamis produced for a steam turbine, which when coupled with an electricgenerator also generates electrical power. Such an electrical powergenerating scheme is known as a “combined cycle” and is highlyefficient. Alternatively, and as illustrated in FIG. 3(b), the cleanfuel gas may be sold to customers (8), for the cement plants, forexample, or other uses. For the types of systems illustrated in FIGS.3(a) and 3(b), chlorine is usually taken out of from the products in thecleaning system before they are directed to the combustion system orsold. Thus, dioxins are not generally formed in such systems.

Depending on the type of post-processing means (2) used in the plant(1), different residues are precipitated in the post-processing means(2), these residues being non-gaseous, and typically solids and/orliquids and/or mixtures thereof. Although the exact composition andphysical form of these residues depends on the type of post-processingmeans (2) and on the composition of the waste processed by the chamber(10), these residues may be divided by any suitable categories,including for example, their physical state (powder, sludge or liquid,for example), by their chemical composition, by the size of particles,and so on. Herein, these residues are conveniently categorized into twotypes of residues, herein denoted Residues 1 (R1) and Residues 2 (R2),as defined hereinbelow.

Residues 1 (R1) may be defined as the residues that are formed only fromthe materials exiting from the chamber (10) via the gas outlet (50), andmay include the products of their subsequent combustion in thepost-processing means (2) (such as for example provided in theapparatuses illustrated in FIGS. 2(a) and 2(b)), and may further includeproducts produced in a gas cleaning means such as a scrubber, forexample, where only water (without additives) is used in the scrubber(such as for example provided in the apparatuses illustrated in FIGS.3(a) and 3(b)).

Thus, Residues 1 (R1) may include mostly components of the treated wasteand condensed vapors which are precipitated in the waste water treatmentsystem (7) in the plants illustrated in FIGS. 3(a) and 3(b), that is,when only water without additives is used in first portion (7′) of thewaste water treatment system (7). Such Residues (1) may include solidparticles and tar (which is present in the products exiting theprocessing chamber), some water and some products formed from thereaction between some materials leaving the processing chamber andwater. For example, the product gases may include hydrogen chloride gas,which may be diluted in the scrubber and form hydrochloric acid, whichmay then react with some solid particles and form salts, some of themsoluble such as NaCl. Scrubber water may react with some components inthe solid particles and may form hydroxides, and thus some of thesesalts and hydroxides may be recycled together with tars and othersolids. In such cases, the Residues 1 (R1) may be in the form of asludge, mixed with water from the waste water treatment system (7).Alternatively, the Residues 1 (R1) may include the materials formingafter the oxidation in the afterburner (3), such as used in the plantsillustrated in FIGS. 2(a) and 2(b), of the raw materials and condensedvapor carried out from the processing chamber. In such plants, someoxides and salts may be present in the raw material, i.e., the waste andadditives which are fed to the processing chamber, and are then carriedout of the chamber; some such materials may not be changed chemically inthe afterburner. On the other hand, some materials may be changedchemically in the afterburner, for example metal to metal oxides,chlorides and so on, depending on the composition of the waste andconditions in the chamber and the afterburner.

Thus, Residues 1 (R1) are formed when the materials exiting theprocessing chamber via the gas outlet (50) are treated in thepost-processing means (2) only with air (and/or oxygen) and/or by water,but without any additives. Thus, if additives or special reagents areused in the post-processing means (2), then Residues (2) are formedinstead, as will be explained further hereinbelow.

Residues 2 (R2), on the other hand, while possibly also includingResidues 1 (R1), are characterized in also including materials whichoriginate from the input of additional substances into thepost-processing means (2), in particular into the gas cleaning systems,and thus may include the actual additives and/or reagents used in thepost-processing means (2), as well as the products of their reactionstherein with materials carried from the processing chamber (10), andtypically may be in the form of a sludge. Such Residues 2 (R2) mayinclude, for the apparatuses illustrated in FIGS. 2(a) and 2(b),reagents such as Ca(OH)₂, Na₂CO₃, NaOH, active carbon and others, whichare used for binding acid gases (including, for example, SO_(x), HCl,HF, P₄O₁₀), and for trapping or adsorbing dioxins and heavy metalcompounds. Products of reactions may include CaCl₂, CaSO₄, Ca₃(PO₄)₂,CaF and/or NaCl, Na₂SO₄, Na₃PO₄, and others. Thus, Residues 2 (R2) mayinclude some oxides and salts (which did not precipitate previously),reagents (since they are usually provided in amounts greater thanrequired), and products of reaction. In the apparatuses illustrated inFIG. 3(a) and FIG. 3(b), part of the waste water is taken out from thefirst part (7′) of system (7), and is directed to the second part (7′)of the cleaning system (7) for special treatment by adding reagents, andby providing filtration and evaporation of solutions. In the second part(7″), Residues (2) are formed, and heavy metals may be transformed intosolid hydroxides (for example, Cu(OH)₂, Mn(OH)₂, and others), andsulphides, including PbS, HgS and others. Chlorine may be transformedinto dry NaCl.

Thus, in the afterburner (3) of FIG. 2(a), some dust (products ofcombustion) is precipitated as Residue 1 (R1). The products ofcombustion, including gases and dust, are directed to a boiler comprisedin the energy generating system (4). Typically, steam is produced in theboiler, though at times hot water may be provided instead for customers,and the steam may be sold or may be used in steam turbine (with electricgenerator) for the generation of electricity. In the boiler some dust isprecipitated too (i.e., as Residue 1 (R1)). Similarly, in the coolingsystem (9) of FIG. 2(b), some dust is also precipitated (i.e., asResidue 1 (R1)), which are also the products of combustion. In theplants illustrated in FIGS. 2(a) and 2(b), Residue 1 (R1) is typicallyin powder form.

Referring to FIG. 2(a), after the boiler in energy generating system(4), the products of combustion (including gases and dust) are directedto the gas cleaning system (5). Reagents, including for example Ca(OH)₂,Na₂CO₃, NaOH, active carbon and/or other reagents, are used here forbinding the acid gases, which may include SO₂, HC1, HF, P₄O₁₀. Productsof reaction between the reagents and the acid gases are formed,including, for example, CaCl₂, CaSO₄, Ca₃(PO₄)₂, CaF and/or NaCl,Na₂SO₄, Na₃PO₄ and others. Hence, Residues 2 (R2) include some oxidesand salts (which did not precipitate previously in the plant (1)), somequantity of reagents (since they are normally fed to the post-processingmeans (2) in amounts greater than the nominal proportions required), andproducts of reaction. Residue 2 (R2) may be in the form of a powder orsludge depending on the type of gas cleaning system (5) that is used.

For example, a “dry” gas cleaning system (5) suitable for the plant (1)illustrated in FIG. 2(a) may include a semi-dry scrubber, into which isfed a suspension of Ca(OH)₂ in water for binding the acid gases. Wateris subsequently evaporated fully, and thus only gases, products Ca(OH)₂,CaCl₂, CaSO₄, Ca₃(PO₄)₂, in powder form, and other dust (which did notprecipitate in the boiler) exit the scrubber. After the scrubber thereis a reactor-adsorber arrangement, wherein a mixture of powders ofCa(OH)₂ and powdered activated carbon (PAC) are fed. These powderedadsorbants have very large specific surface values (typically carbon>750m²/g; Ca(OH)₂>30 m²/g), and the Ca(OH)₂ may adsorb the remaining acidgases, while the PAC adsorbs dioxins and components containing heavymetals. After the reactor-adsorber there is a fabric filter arrangementwhere Residues 2 (R2) may be precipitated, including Ca(OH)₂, activecarbon, dioxins, some oxides and salts (which did not precipitatebefore), and products of reaction (CaC1₂, CaSO₄, Ca₃(PO₄)₂ and othersubstances). Essentially, gas carrying dust, which includes toxiccomponents such as dioxins, heavy metals and their oxides and salts, isfiltered through the layer of dust precipitated on the fabric of thebags and including adsorbents such as for example Ca(OH)₂ and PAC, andthe toxic components are adsorbed and thus precipitate out of thecarrier gas. The clean gas obtained after filtration is directed to anexhauster and then to the stack (6) for expulsion into the atmosphere.Residues 2 (R2) obtained from such a cleaning system (in particular fromthe bag filter arrangement) do not include liquid, and thus such systemsare known as “dry” cleaning systems. Residues 2 (R2) are very toxic andmay include dioxins, compounds of heavy metals and Ca(OH)₂, activecarbon, some oxides and salts (which did not precipitate previously),products of reaction (such as, for example, CaCl₂, CaSO₄, Ca₃(PO₄)₂ andother substances). However, since this Residue 2 (R2) is hygroscopic(especially the CaCl₂ portion thereof), it may absorb water from thewater vapour that is generated along with other combustion products, andthus may have a sludge-type consistency. Accordingly, in many instancestubes which are used for transporting this Residue 2 (R2) in the gascleaning system (5) are heated to enable the Residue 2 (R2) to dry.

On the other hand, and referring to the post-processing means (2)illustrated in FIG. 2(b), atomized water, or water suspension withCa(OH)₂, or water solution of Na₂CO₃ or of NaOH may be used in thecooling system (9). When water is used, cooling system (9) acts only asa cooler, and Residues 1 (R1) are precipitated therein. When water withreagents is used (for binding the acid gases —SO_(x), HC1, HF, P₄O₁₀)the cooling system (9) also functions as a cooler, but additionally alsoforms simultaneously part of the cleaning system. In the latter case,Residues 2 (R2) are precipitated, and a reactor adsorber and bag filterarrangement may be provided, as described with respect to thearrangement of FIG. 2(a), mutatis mutandis.

Referring to the post-processing means (2) of the plants illustrated inFIG. 3(a) and FIG. 3(b), the gas cleaning system (5′) may comprise, forexample, scrubbers and other means wherein the following materials areremoved from the product gases: H₂O, HCl, H₂S, NH₃, HF, oils, tars, dustand others. Waste water or waste aqueous solutions previously used inscrubber is transported to a waste water treatment system (7) forcooling and cleaning before being recycled to the gas cleaning system(5). Residues 1 (R1), comprising oils, tars and dust including fly ash,and even some reagents and products of reaction, are precipitated in afirst portion (7′) of the waste water treatment system (7), and therecycled waste water is reintroduced into the gas cleaning system (5′).Part of waste water is taken out from the first part (7′) of the wastewater treatment system (7) and is channeled to the second part (7″)thereof. This water contains an accumulation of components includingheavy metals, chlorine compounds and others, and in the second part (7″)of the waste water recycling system (7″) heavy metals are transformedtypically to solid hydroxides (such as, for example, Cu(OH)₂, Mn(OH)₂and others) and to solid sulphides (such as, for example, PbS, HgS andothers), and concurrently, Chlorine may be transformed in dry NaCl, forexample. These solid residues are Residue 2 (R2).

Thus, in essence, such plasma-based processing plants of the artgenerate Residues 1 (R1) and Residues (R2), regardless of the specificdetails of the post-processing means (2), and a problem commonlyencountered relating to the operation of such plasma-based processingplants (such as for example each one of the four prior art casesexemplified above) is the safe and economic disposal of the Residues 1(R1) and Residues 2 (R2) obtained with the prior art post-processingmeans.

Particularly where the waste has a large proportion of heavy metals,dioxins and many other volatile materials (including some metals, metaloxides, chlorides, fluorides and others e.g., Cd, Hg, As, Zn, CdO, K₂O,Na₂O, CuO, CuCl, CdCl₂, HgCl₂, PbCl₂, AsCl₃, NiCl₂, ZnCl₂, MnCl₂, andothers) that have low boiling points and are thus vaporized in thechamber (10), these materials are entrained with the product gases,rather than being included in the slag. These volatile components willbe eventually accumulated in the post-processing means (2), andparticularly in the gas cleaning system, and can not be treated furtherin the prior art plants. As this can lead to unacceptable high levels oftoxic components delivered to the stack (6), these residues must beremoved for disposal, typically by land filling in the prior art.

In some prior art plants, the problem of disposal of Residues 1 (R1) isaddressed by mixing the Residues 1 (R1) with water, drying this mixtureand granulating the same. The granules are then fed to a separatespecialized and dedicated plasma-based processing plant. However, thisdoes little to solve the problem, since because of their composition andstructure many granules are crushed during feeding and may be carriedout by product gases again, or may be vaporized before reaching the hotzone of the plant, which thus results in a need for further, andpossibly endless, recycling.

In another system (“The Plasma Treatment of Incinerator Ashes”, by D. M.Iddles, C. D. Chapman, A. J. Forde, C. P. Heanly, of Tetronics Ltd.) flyash obtained from reciprocating grate incinerator and a fluidised bedwas fed to an apparatus via the upper end of the apparatus. Theapparatus is described as having a twin DC plasma arc heating system,such as to melt the feed. The apparatus produces a slag which may be auseful vitrified product, organic species are claimed to be destroyed,and gas treatment is required to deal with the gases produced. Whilesuch an apparatus may be an improvement over other prior art systems,the fly ash has to be separately transported and fed into the apparatus,adding cost and complexity to the conversion of the original municipalsolid waste (MSW) or the sewage sludge waste (SSW). There is nosuggestion that such an apparatus should be incorporated in a regularwaste processing plant. Nevertheless, even if such a combination wereformed, the apparatus would still add significant operating costs due tothe plasma torches and so on. Further, in the apparatus disclosed, flyash may still be entrained with product gases and removed from theprocessing chamber, and similarly volatile components in the fly ash arevaporized before reaching the hot zone, since the fly ash is introducedat the cooler end of the apparatus. Such prior art systems are also notsuitable for dealing with Residues 2 (R2), in any case. The hightemperatures of the apparatus destroys sulphates such as CaSO₄ andNa₂SO₄ to SO_(x) again. The SOx then needs to be bound again in aspecial gas cleaning system, where additional residues will be formed.

It is therefore an aim of the present invention to provide a system andmethod for dealing with non-gaseous residues produced in a wasteconverting plant, in particular plasma-torch based plants, whichovercomes the limitations of prior art plants.

It is another aim of the present invention to provide such a system andmethod that may be incorporated into a municipal solid waste processingapparatus.

It is another aim of the present invention to provide such a system thatis relatively simple mechanically and thus economic to incorporate intoa processing plant design.

It is another aim of the present invention to provide such a systemincorporated as an integral part of a plasma-torch based type wasteconverter.

It is also an aim of the present invention to provide such a system thatis readily retrofittable with respect to at least some existingplasma-torch based waste converters.

The present invention achieves these and other aims by providing asystem and method for redirecting non-gaseous residues, in particularResidues 1 and/or Residues 2, directly to the hotter parts of theprocessing chamber. In one embodiment this is accomplished by providinga reservoir for collecting residues precipitated by the post-processingmeans, and providing communication between the reservoir and the hotterpart of the processing chamber by means of a direct connecting conduit.Means are then provided for transporting the residues into the chamber.In another embodiment, the residues are mixed with suitable additives,including slag produced by the processing chamber, and cementingadhesive or the like to form composite pellets or granules which aredesigned to be stable in the upper cooler part of the processingchamber. These pellets are then fed to the processing chamber via thetop thereof with or without other regular waste. However, the majorityof the residues inside the granules cannot be carried out by gases fromthe chamber or be chemically destroyed until the granules reach the hightemperature regions of the chamber. Thereat, the residues inside thecomposite pellets are melted and/or possibly interact with slag and/orwith additives inside the granules. So, part of the toxic components ofresidue will be destroyed, and part will be included in the molten slag,collected via a suitable reservoir. In other embodiments, both types ofsystems may be incorporated, and operated, separately or jointly.

The effect of introducing the residues into the high temperature zone ofthe processing chamber is to avoid some of the toxic compounds merelyexiting the processing chamber relatively intact. Rather, some of themetal oxides which have low boiling points may interact with the slagand/or additives existing in the granules at the lower end of theprocessing chamber, forming solid solutions which have a much highermelting point than that of its components. In this way, at least some ofthe heavy metals (including for example Cd, Zn and Pb) may be includedin the vitrified slag, and thus prevented from contaminating theenvironment either as part of the gases leaving the stack (6) or in byway of burial of residues in a landfill. Similarly, dioxins comprised inthe residues, when introduced to the high temperature zone of thechamber (10), are reduced to HCl, CO and hydrocarbons, which aresubsequently pyrolysed and oxidized in the gasification zone of thechamber (10) to generate CO.

It is important to note that the present invention comprises a wasteprocessing chamber that is adapted to accommodate a column of waste andto enable the waste to migrate through the chamber in a downstreamdirection. The column of waste between the hot zone (that is provided bythe plasma torches) and the gas outlet provides a tortuous matrixstructure for gases that are formed in the gasification process, so thatthe escape of gases from the chamber is substantially retarded. Thisgives an opportunity for slag and other substances flowing downwardsthrough the chamber to interact with residues being carried by thegases, as explained above, to the gas outlet. The position of the gasoutlet in relation to the melting zone is thus also important in thecontext of the present invention. In the absence of a column of waste,or where the gas outlet is not upstream of the hot zone, the gasescarrying the residues are substantially freely vented from the chamber,and cannot effectively interact with slag or other materials that areinput to the processing chamber. Furthermore, the column of waste helpsto maintain quasi steady state conditions within the processing plant,and a stable temperature profile is also maintained therein, comprisinga relatively cooler upper zone, herein the gasification zone, whereorganic material is gasified, and a lower hotter zone, herein themelting zone, in which substantially all the inorganic materials areconverted into molten metals and non-metallic inorganic slag, close tothe plume generated by the plasma torches of the processing chamber. Asinorganic waste in the downstream part of the column is melted, and asorganic waste in the upper part is gasified, the waste in the columngradually migrates towards the downstream end, and more waste may beinput into the chamber. This, however, does not substantially affect thequasi-steady state conditions referred to above. The conditions providedin the melting zone include sufficient temperature and residence time,such that the slag is sufficiently melted so that when it is removedfrom the chamber and subsequently cooled it forms solidified fused slag.However, the melting zone may also be adapted to be a vitrificationzone, in which the conditions, i.e., temperature and/or residence timeare increased sufficiently such that at least part of the slag isvitrified, and thus has a glassy, non-crystalline structure aftersolidification outside of the chamber.

CH 691507 relates to a method, and device, for burning solid or viscousmaterial in grate firing unit. The method involves delivering materialto a grate (2) and burning it. Hot gases are conducted through furtherunits (9, 12, 15, 20), in which pollutants in the gases are at leastpartly separated out. The unburned material is conducted as slag to aslag remover (3). The pollutant residues are collected from the gases,which are preferably passed through a steam boiler (9) and a mixer (12)to remove pollutants, and the pollutants returned to the grate. Thisarrangement supposedly has advantages of high combustion efficiency withreduced residual waste and pollutant levels.

In the first place, this reference is concerned with the combustion ofmaterials using a grate firing unit. This is very different from a hightemperature (typically plasma-based) waste processing plant, in whichthe conditions include higher working temperatures and residence timessuch as to melt metals therein. Further, the pollutants of thisreference are introduced between two portions of the grate, and it isunclear whether this is actually the high temperature zone provided bythe combustion process therein. Furthermore, the grate arrangement, ifused with plasma torches instead of a combustion system would result inmolten slag being deposited onto the grate, which would thus becomedogged and inoperative, and/or in the grate itself melting. Inparticular, the disclosed device of this reference is not adapted foraccommodating a column of waste—rather, waste is fed onto the grate andburned thereon. Also, the gases are removed well downstream of thegrate, and therefore cannot in any case interact with the waste or anyother material that is being input to the chamber. Accordingly, theadvantages of the present invention are not so readily achievable withthe device and method of this reference. Finally, there is no disclosureat all of the pollutants being provided in the form of pellets via thewaste inlet of the incinerator.

WO 89/09253 relates to a method and device for the incineration ofrefuse. Flyash produced by incineration in the plant (and optionallyother sources) is introduced into the refuse being incinerated. Incontrast to the present invention, though, the flyash is introduced atthe cold upper part of the chute, at a location where the temperature isabout 20° C., rather than in the hot kiln. Furthermore, the flyash isintroduced as powder, or as a sludge, mixed with a liquid, and not inpellets of the type of the present invention. Hence, this referenceneither discloses nor suggests the present invention. Moreover, theincinerator of the reference does not comprise a gas outlet upstream ofthe kiln, and if it were to be fitted with plasma torches and a gasoutlet in the waste processing chamber, the flyash would continue to beejected out therefrom via the gas outlet. In the reference, gas ispassed from the downstream end of the kiln to an electrostatic filtervia a baffle and boiler. This reference therefore does not disclose orsuggest the present invention.

EP 324 454 relates to a method for cleaning the smoke gases from largecombustion units, in which the largest part of the solid matter carriedby the smoke gases (flue ash) is separated by dry dust filtering (9),the remaining solid matter is precipitated in a subsequent acid smokegas scrubber (10) and wherein the solid matter in the dry dust filteringis melted down possibly together with waste and/or admixtures melting toglass and the solid matter elutriated in the smoke gas scrubbing isextracted and filtered. The method is directed to combustion unitsrather than to high temperature (plasma-torch) based processing plants.Further, there is no disclosure or suggestion of the combustion unitbeing adapted for accommodating a column of waste, or of the flyashbeing input into the high temperature zone of the combustion unit, or offorming the flyash into pellets for feeding into the top of thecombustion unit together with waste, in contrast to the presentinvention. Even less so is there any suggestion of slag being recycledinto the combustion unit.

U.S. 2002/006372 relates, inter alia, to a waste treatment equipment andmethod in which waste is passed from a low temperature horizontal typerotary drum furnace, to a high temperature combustion melting furnace,and water insoluble constituents k are returned to the low temperaturefurnace, while solid residues therefrom (not carried by gas) are fedinto the high temperature melting furnace. Thus, this reference does notdisclose a processing chamber as in the present invention—indeed therotary furnace by definition cannot accommodate a column of waste—andthe gas-borne residues are eventually input to the low temperaturefurnace, rather than the hotter melting furnace. There is also nodisclosure or suggestion that the dust collected by dust collectors isto be directly input to the high temperature region of the meltingfurnace. Finally, there is no suggestion or disclosure of the residuesbeing formed into pellets, or of these and/or slag being fed at thecooler end of the furnace in the manner of the present invention.

WO 99/23419 relates to an explosion-proof, closed reaction chamber fordisposal of objects containing explosive material. The chamber has avacuum aperture, through which after the reaction is completed gases andeasily movable reaction products can be sucked away. The inner surfacehas a temperature-resistant lining with a protection against splinters.The feed device comprises a movable floor aperture. The floor ishydraulically driven. An ignition device comprising a gas flameactivates desired rapid reactions. It can also comprise an electricallight arc. A shock and thrust absorber consists of a large metal bodyand a second absorber device for thrust loads is incorporated in theupper side of the chamber. The chamber itself is thus not adapted foraccommodating a column of waste, nor are there any residues that areinput into the chamber. Rather, gases are transferred from the chambervia the upper opening to a plasma chamber, and eventually, residuesoriginating from the plasma chamber and from the reaction chamber arereintroduced to a sluice. Thus, in contrast to the present invention,the plasma chamber is not for processing waste, nor is it adapted foraccommodating a column of waste, but rather only accepts gaseousproducts from the reaction chamber. Further, there is no suggestion ofthe residues being provided to the hot zone of the plasma chamber, butare instead provided to the sluice. There is absolutely no hint of theresidues being formed into high temperature pellets, nor of these or theslag being reintroduced to the plasma chamber via the upper cooler endthereof, in contrast to the present invention.

FR 2691524 relates to the disposal of radioactive graphite withoutcontaminating the environment, by pulverising, mixing with water andburning, then purifying combustion gases and recycling unburnt solids.Graphite pieces are crushed and powdered in two stages to less than 200microns particle size, then mixed with water and emulsifying and wettingagents to form a suspension. This. suspension is pumped through a heater(E) to a two-stage burner and the resulting combustion gases arepurified before release to the environment, by passing throughcylone(s), gas-washing system and absolute filter. Solids recovered fromstages and are recycled to mixer. Gases may be cooled in heat exchangerbefore the washing stage, to recover some combustion heat.Alternatively, the gases are cooled by finely sprayed water. In eithercase gases are reheated to 80° C. before the final filtration. Thus,this reference merely relates to residues being reintroduced into theburners together with the “waste”, in other words, there is no teachingat all of introducing the residues directly at the hot zone of theburners, or in the form of high temperature pellets with the waste.

DE 4333510 relates to a process for removing dust and toxic substancesfrom hot gases. The process comprises introducing gases into a gascooler, removing dust by a hot gas filter and passing through boiler andgas washer before release to the atmosphere. Hot dust-laden toxic gasesarise from the combustion of liquid paste and solid residues in arotating furnace and an afterburner chamber, and are then discharged toan assembly where they are treated. The hot gases are first introducedat 1200° C. into a gas cooler, where they cool to 800° C. before thedust is removed by a hot gas filter. The hot dust-free gases are thenpassed through a boiler where they surrender heat and generate steam.The hot gases are then passed through a gas washer before release to theatmosphere. The process removes substances from the gases whichotherwise have a severe detrimental effect upon the system componentsthrough which they pass. Thus, this reference merely relates to dustresidues being reintroduced into the rotating furnace together with theoriginal waste, in other words, there is no teaching at all ofintroducing the residues at the hot zone of the furnace.

SUMMARY OF INVENTION

The present invention relates to a residues recycling system forrecycling at least part of the residues formed in a waste processingplant, said waste processing plant having:—

-   -   at least one waste processing chamber adapted for accommodating        a column of waste and for enabling said waste to migrate through        the chamber in a downstream direction, said chamber having at        least one upstream gas outlet means and further having high        temperature generating means adapted for providing a high        temperature melting zone in a downstream part of said chamber        and a relatively cooler upstream gasification zone, wherein said        melting zone is at conditions at least sufficient for enabling        substantially all inorganic waste therein to be melted into at        least one of melted metals and slag, and wherein said upstream        gasification zone is at conditions sufficient for enabling        gasification of organic waste in said column of waste;    -   at least one post processing means operatively connected to said        at least one waste processing chamber, wherein said        post-processing means are adapted for enabling said residues to        be collected therefrom during operation of said at least one        waste processing chamber;    -   wherein said residues recycling system is characterized in being        adapted for collecting said at least part of the residues from        said post processing means and for introducing at least a        portion of said at least part of the residues into said        processing chamber such that during operation of said system        said portion of said at least part of the residues is exposed to        said high temperature melting zone provided by the said high        temperature generating means.

The recycling system preferably comprises at least one collectionreservoir operatively connected to said post processing means andadapted for collecting at least part of the residues therefrom.

The residues typically comprise at least two types of residues,including residues 1 and residues 2 which differ one from the other inat least their chemical properties, that are separately collectible fromsaid post processing means, and said system comprises at least one saidcollection reservoir for separately collecting one or another of saidresidues 1 and residues 2.

In a first and third embodiments, the recycling system typicallycomprises suitable conduit means for providing communication betweensaid at least one collection reservoir and said lower part of said atleast one processing chamber, said conduit means adapted fortransporting said residues from said at least one collection reservoirto said lower part of said at least one processing chamber for directexposure of said residues to said hot zone during operation of saidsystem. The system may further comprise suitable transport meansoperatively connected to said at least one collection reservoir forassisting transportation of said residues through said conduit means.The transport means may comprise a suitable fluid medium fortransporting the said residues.

The system may further comprise suitable mechanical transport meansoperatively connected to said at least one collection reservoir forassisting transportation of said residues through said conduit means,and the transport means may comprise a suitable pump for transportingthe said residues. The conduit means may comprise at least one suitableoutlet operatively connected to said lower part of said processingchamber. The conduit means may comprise at least one suitable valveoperable to enable the flow of at least a portion of said residuesthrough said conduit means to be selectively prevented or allowed. Thevalve may be operatively connected to a suitable control system. Thecontrol system may be further operatively connected to at least onesuitable sensor comprised in said post processing means and adapted forcontrolling the operation of said valve according to predeterminedconditions sensed by said sensor.

In a second and third embodiments, the residues recycling systemcomprises a source of suitable additives and a suitable mixer for mixingat least a portion of said residues with said additives, said additivesadapted for at least partially encapsulating said portion of residues ina matrix that is thermally and mechanically stable at temperaturessubstantially lower that the temperature of said melting zone, firstgranulating means for granulating said matrix into residue granules, andmeans for transporting said residue granules to a suitable inletcomprised in the cooler part of said at least one processing chamber.The additives may be chosen from any one or combination of cement,sodium silicate, organic compounds including thermoplastics, andinorganic compounds and/or complexes including oxide powders, oxidesolutions, salt powders and salt solutions. The said inlet is typicallya waste inlet for enabling waste to be input into said at least oneprocessing chamber. The additives may comprise at least part of saidslag, and the system may further comprise means for introducing at leastpart of said slag into said mixer. The system may also further comprisesuitable transport means for transporting slag produced by said at leastone processing chamber to said mixer. The system may further comprisesuitable transport means operatively connected to said at least onecollection reservoir for assisting transportation of said residuesOptionally, the transport means comprises a suitable fluid medium fortransporting the said residues at least to said mixer.

The recycling may further comprise suitable mechanical transport meansoperatively connected to said at least one collection reservoir forassisting transportation of said residues at least to said mixer.Optionally, the transport means comprises a suitable pump fortransporting the said residues.

The recycling system may further comprise at least one suitable valveoperable to enable the flow of at least a portion of said residues tosaid mixer to be selectively prevented or allowed Preferably, the valveis operatively connected to a suitable control system. Advantageously,the control system is further operatively connected to at least onesuitable sensor comprised in said post processing means and adapted forcontrolling the operation of said valve according to predeterminedconditions sensed by said sensor.

The volume (Vg) and external surface area (Fg) of at least a portion ofsaid residue granules may be chosen such that:Vg/Fg≧0.00002*Hwherein H is a predetermined linear distance that is correlated to thetravel distance of the residue granules from the upper part of theprocessing chamber to the lower part thereof.

H may comprise the height of the said processing chamber taken from thecenter of the said gas outlet to the centre of the slag outlet portcomprised in said lower part and adapted for enabling the molten slag toexit the said processing chamber. Alternatively, H comprises thevertical distance taken from the center of the said gas outlet to anominal level of the surface of the molten slag at the said lower partof the said chamber. Alternatively, H comprises the vertical distancetaken from the center of the said gas outlet to said high temperaturezone of said lower part of said processing chamber. Alternatively, theprocessing chamber comprises at least one plasma torch means and Hcomprises the vertical distance taken from the center of the said gasoutlet to the center of the output end of said at least one plasmatorches means.

At least a portion of said slag may be removed from said chamber andsubsequently cooled to provide solidified fused slag. Preferably, saidconditions in said melting zone provided by said high temperaturegenerating means are sufficient such that said melting zone is also avitrification zone, and at least a portion of said slag may be removedfrom said chamber and subsequently cooled to provide solidifiedvitrified slag.

The residues recycling system according to all embodiments optionallyfurther comprises a slag recycling system for at least part of the slagformed in a waste processing plant and subsequently cooled andsolidified after extraction therefrom, wherein said slag recyclingsystem comprises a suitable converting means for converting at leastpart of said solidified slag into slag particles, and means fortransporting at least a part of said slag particles to a suitable inletcomprised in the cooler part of said at least one processing chamber.Preferably, the said inlet is a waste inlet for enabling waste to beinput into said at least one processing chamber. Preferably, the systemfurther comprises means for introducing suitable additives into saidconverting means.

The volume (Vr) and surface area (Fr) of at least a portion of said slagparticles may be chosen such that:Vr/Fr<Vg/Fgwherein (Vg) is the volume and (Fg) is the external surface area of theresidue granules provided by said recycling system.

In one application of the present invention, the high temperaturegenerating means comprises at least one plasma torch means comprising anoutput end extending into a lower part of said waste processing chambersaid at least one plasma torch means adapted for providing a hightemperature melting zone in a lower part of said chamber at leastsufficient for enabling substantially all inorganic waste accommodatedtherein to be melted.

The present invention also relates to a waste processing plantcomprising:—

-   -   at least one waste processing chamber adapted for accommodating        a column of waste and for enabling said waste to migrate through        the chamber in a downstream direction, said chamber having at        least one upstream gas outlet means and further having high        temperature generating means adapted for providing a high        temperature melting zone in a downstream part of said chamber        and a relatively cooler upstream gasification zone, wherein said        melting zone is at conditions at least sufficient for enabling        substantially all inorganic waste therein to be melted into at        least one of melted metals and slag, and wherein said upstream        gasification zone is at conditions sufficient for enabling        gasification of organic waste in said column of waste;    -   at least one post processing means operatively connected to said        at least one waste processing chamber, wherein said        post-processing means are adapted for enabling said residues to        be collected therefrom during operation of said at least one        waste processing chamber, and characterized in further        comprising a residues recycling system as herein defined.

The post-processing means may comprise a suitable afterburner, asuitable energy utilization means, a suitable gas cleaning system and asuitable stack operatively connected in series to said processingchamber.

Alternatively, the post-processing means comprises a suitableafterburner, a combustion products cooling system, a suitable gascleaning system and a suitable stack operatively connected in series tosaid processing chamber.

Alternatively, the post-processing means comprises a suitable gascleaning system, a suitable energy utilization means and a suitablestack operatively connected in series to said processing chamber, andfurther comprises a waste water treatment system operatively connectedto said gas cleaning system.

Alternatively, the post-processing means comprises a suitable gascleaning system and a waste water treatment system operatively connectedto said gas cleaning system, and wherein said gas cleaning system isadapted for channeling clean fuel gases therefrom to an external user.

In one application of the present invention, the waste processing plantis a plasma torch based plant, and the high temperature generating meanscomprises at least one plasma torch means comprising an output endextending into a lower part of said waste processing chamber said atleast one plasma torch means adapted for providing a high temperaturemelting zone in a lower part of said chamber at least sufficient forenabling substantially all inorganic waste accommodated therein to beconverted into at least one of molten metal and slag.

The present invention also relates to a method for recycling at least apart of residues formed in a waste processing plant, said wasteprocessing plant having:—

-   -   at least one waste processing chamber adapted for accommodating        a column of waste and for enabling said waste to migrate through        the chamber in a downstream direction, said chamber having at        least one upstream gas outlet means and further having high        temperature generating means adapted for providing a high        temperature melting zone in a downstream part of said chamber        and a relatively cooler upstream gasification zone, wherein said        melting zone is at conditions at least sufficient for enabling        substantially all inorganic waste therein to be melted into at        least one of melted metals and slag, and wherein said upstream        gasification zone is at conditions sufficient for enabling        gasification of organic waste in said column of waste;    -   at least one post processing means operatively connected to said        waste processing chamber, wherein said post-processing means are        adapted for enabling said residues to be collected therefrom        during operation of said at least one waste processing chamber;    -   wherein said method comprises the steps:    -   collecting at least part of said residues from a said post        processing means; and    -   introducing at least part of said residues into a said        processing chamber such that during operation of said system        said residues are exposed to said high temperature melting zone        provided by the said high temperature generating means.

Optionally, in step (a), said residues are collected in at least onesuitable collection reservoir operatively connected to said postprocessing means.

Typically, the residues comprise at least two types of residues,including residues 1 and residues 2 which differ one from the other byat least their chemical properties, that are separately collectible fromsaid post processing means, and wherein in step (a) residues 1 andresidues 2 are separately collected in different said collectionreservoirs.

Optionally, in step (b), said residues are transported from said atleast one collection reservoir to said lower part of said at least oneprocessing chamber for direct exposure of said residues to said hot zoneduring operation of said system.

Optionally, in step (b), suitable additives are mixed with at least aportion of said residues, said additives being adapted for at leastpartially encapsulating said portion of residues in a matrix that isthermally and mechanically stable at temperatures substantially lowerthat the temperature of said hot zone, said matrix is granulated intosuitable residue granules, and said residue granules are transported toa suitable inlet comprised in the cooler part of said at least oneprocessing chamber for introduction into the said at least oneprocessing chamber. Advantageously, the volume (Vg) and external surfacearea (Fg) of at least a portion of said residue granules are chosen suchthat:Vg/Fg≧0.00002*Hwherein H is predetermined linear distance that is correlated to thetravel distance of the residue granules from the upper part of theprocessing chamber to the lower part thereof.

Preferably, H comprises the height of the said processing chamber takenfrom the center of the said gas outlet to the centre of the slag outletport comprised in said lower part and adapted for enabling the moltenslag to exit the said processing chamber.

Alternatively, H comprises the vertical distance taken from the centerof the said gas outlet to a nominal level of the surface of the moltenslag at the said lower part of the said chamber.

Alternatively, H comprises the vertical distance taken from the centerof the said gas outlet to said high temperature zone of said lower partof said processing chamber.

Alternatively, the processing chamber comprises at least one plasmatorch means and H comprises the vertical distance taken from the centerof the said gas outlet to the center of the output end of said at leastone plasma torches means.

Optionally, the method further comprises the step (c) of introducingslag granules to a suitable inlet comprised in the cooler part of saidat least one processing chamber for introduction into the said at leastone processing chamber, said slag granules being produced by granulatingat least a portion of the slag provided by the said processing chamberduring operation thereof. Preferably, the volume (Vr) and surface area(Fr) of at least a portion of said slag granules are chosen such that:Vr/Fr<Vg/Fgwherein (Vg) is the volume and (Fg) is the external surface area of theresidue granules provided in step (b).

In said method, components of said residues may be introduced into slag,particularly the recycled slag, which is subsequently removed from saidapparatus and subsequently cooled and solidified to trap therein saidcomponents. These components may include any one or more of Cd, Zn, Pb,Cu, Tl, Hg, Sb, As, Cr, Mn, Ni, V, Cl, S, P, F, in elemental form or incompounds. The conditions in said hot melting zone are preferably suchthat the said slag is vitrified thereat.

In the method, components of said residues may form solid solutions withsaid slag, which is subsequently removed from said apparatus andsubsequently cooled and solidified to form vitrified slag. Thesecomponents may include one or more of Hg, S, C1, As, Se and oxides ofmetals: Cr, Ni, Mn, Co, Mo (3-5%); Ti, Cu, F, La, Ce, Cd, Th, Bi, Zr(5-15%); Li, B, Na, Mg, K, Ca, Fe, Zn, Rb, Cs, Sr, Ba, U; A1, Si, P, Pb.

DESCRIPTION OF FIGURES

FIG. 1 shows schematically the general layout and main elements of atypical waste plasma processing apparatus of the prior art.

FIGS. 2(a), and 2(b) illustrate schematically the general layout andmain elements of two derivatives of one type of a typical wasteprocessing plant of the prior art, including the apparatus of FIG. 1 andpost-processing elements.

FIGS. 3(a) and 3(b) illustrate schematically the general layout and mainelements of two derivatives of another type of a typical wasteprocessing plant of the prior art, including the apparatus of FIG. 1 andpost-processing elements.

FIG. 4 shows schematically the general relationship between the mainelements of a first embodiment of the present invention.

FIG. 5 shows schematically the general relationship between the mainelements of a second embodiment of the present invention.

FIG. 6 shows schematically the general relationship between the mainelements of a third embodiment of the present invention.

FIG. 7 shows schematically the general layout and main elements of afirst embodiment of the present invention.

FIG. 8 shows schematically the general layout and main elements of asecond embodiment of the present invention.

FIG. 9 shows schematically the general layout and main elements of athird embodiment of the present invention.

FIG. 10(a) and FIG. 10(b) illustrate in fragmented transversecross-section view the relative positions of the outlet of the directfeed system and the plasma torches of the embodiments of FIGS. 3 and 5,according to two different processing chamber configurations.

DISCLOSURE OF INVENTION

The present invention is defined by the claims, the contents of whichare to be read as included within the disclosure of the specification,and will now be described by way of example with reference to theaccompanying Figures.

The present invention relates to a system for recycling non-gaseousresidues, generated by a waste processing apparatus, in order to reducethe eventual volume of residues and to dispose of at least a part of theheavy metals, produced by the waste converting apparatus, by encasingthe compounds and complexes of metals in the slag melt, i.e., while theslag is still molten. The recycling system is characterized in that theresidues are redirected to the apparatus in such a manner as to reachthe hotter parts of the processing chamber of a waste convertingapparatus for processing thereof at the higher temperature zones of theapparatus, that is, the melting zone, without being substantiallyaffected by the lower temperature gasification zones thereof. Thepresent invention is also directed to such waste converting apparatushaving the aforesaid system, and to methods of operating such systemsand apparatuses.

The term “downstream” refers to a direction along the direction of flowof waste in the processing chamber from the waste inlet to the meltingzone, while “upstream” refers to a direction substantially opposedthereto. With reference to other parts of the apparatus, the term“downstream” refers to a direction along the direction of flow ofmaterial in the part of the apparatus, while “upstream” refers to adirection substantially opposed thereto.

The term “waste converting apparatus” herein includes any apparatusadapted for treating, processing or disposing of any waste materials,including municipal waste (MSW), household waste, industrial waste,medical waste, sewage sludge waste (SSW), radioactive waste and othertypes of waste, in particular by means of plasma treatment.

The term “slag” herein refers primarily to the inorganic, non-metallicmaterial that collects at the bottom end of the waste processingapparatus in a substantially molten state after it has been treated bythe heat generating means, particularly in the form of plasma torches.Nevertheless, the term “slag” herein may also include a mixture of suchslag and metals, and also a suspension of metal particles in such slag.The term “fused slag” relates herein to slag that was formed in such anapparatus, and subsequently solidified after cooling.

The term “vitrification” relates to the formation of slag in a glassy ornon-crystalline form, wherein the temperature and/or residence time issufficient such that the inorganic waste is fully melted.

The term “residues” herein refers to non-gaseous materials that areprecipitated or otherwise extracted downstream (that is along thedirection of flow of gases away from the processing chamber) of the gasoutlet of the processing chamber, particularly in the post-processingmeans operatively connected thereto. Such residues are hereinsubcategorized as Residues 1 (R1) and Residues 2 (R2). Residues 1 (R1)are herein defined as the residues that originate from the wasteprocessing chamber of the apparatus and are entrained therefrom bygases, and/or residues that originate as a result of the subsequentcombustion process in the post-processing means. In other words,Residues 1 (R1) are formed when the materials exiting the processingchamber via the gas outlet are treated in the post-processing means onlywith air (and/or oxygen) and/or by water, but without any additives.Residues 2 (R2) are characterized in also comprising materials whichoriginate from the input of additional substances into thepost-processing means (such as for example additional reagents andproducts of their reactions), in particular the gas cleaning systems,but may possibly also include Residues 1 (R1) mixed therein In otherwords, if additives or special reagents are used in part of thepost-processing means, then Residues 2 (R2) are formed in this part ofthe post-processing means, and/or downstream thereof.

The term “post processing means” refers to any apparatus or systemoperatively connected to the waste processing chamber of the apparatus,in particular the gas outlet thereof, and adapted for the furtherprocessing of product gases generated by the waste processing chamber.

Referring to the Figures, FIGS. 4, 5, and 6 illustrate schematically afirst, second, and third embodiments of the present invention. A postprocessing means (200) is operatively connected to at least one wasteconverting apparatus (10) via a gas outlet line (101) at the gas outlet(50) of the apparatus (10), and in fact one (or more) post-processingmeans may be operatively interconnected to one or a plurality of saidapparatus (10) in any desired permutation or combination, in a mannersimilar to that described herein with respect to the operativeconnection between single post-processing means and a single processingchamber, mutatis mutandis. The post-processing means (200) may be anytype of post processing means that may be connected to the apparatus topost-process the product gases, and that generates therein Residues 1(R1) and/or Residues 2 (R2), and thus may include any one of thepost-processing means (2) illustrated in FIGS. 2(a), 2(b), 3(a) and3(b), for example.

Referring to FIG. 4, in the first embodiment of the present invention,the residues recycling system (900) according to the invention is in theform of a direct feed system (700), configured to directly channel theresidues precipitated in the gas processing means (200) to the chamber(10).

Referring to FIG. 5, in the second embodiment of the present invention,the residues recycling system (900) is in the form of a indirect feedsystem (800), configured to encapsulate the residues in a thermally andmechanically protecting matrix of slag and other additives, and to thenchannel the encapsulated residues to the chamber (10).

Referring to FIG. 6, in the third embodiment of the present inventionthe residues recycling system (900) comprises both the direct feedsystem (700) and the indirect feed system (800), substantially as forthe first and second embodiments, respectively, mutatis mutandis.

Hereinafter, the first, second and third embodiments of the presentinvention are described in greater detail in the context of the type ofpost-processing means illustrated schematically in FIG. 2(a). Clearly,though, the residue recycling system (900) according to any of theseembodiments is similarly applicable to any other type of post-processingmeans (200) that is operatively connected to the outlet (50) andproduces non-gaseous residues, including for example the post-processingmeans illustrated in FIGS. 2(b), 3(a), 3(c), mutatis mutandis.

Thus, and referring to FIGS. 7, 8 and 9, in each of the correspondingfirst, second and third embodiments, respectively, the plasma wasteprocessing converting apparatus or plant, designated by the numeral(100), comprises a processing chamber (10), the upstream upper portion(14) of which, while typically is in the form of a cylindrical orfrusta-conical vertical shaft, may be in any desired shape.

It is important to note that in the present invention, the wasteprocessing chamber (10) is adapted to accommodate a column of waste. Thecolumn of waste between the hot zone (that is provided by the plasmatorches) and the upstream gas outlet provides a tortuous matrixstructure for gases that are formed in the gasification process, so thatthe escape of gases from the chamber is substantially retarded. Thisgives an opportunity for slag and/or other substances flowing downwardsthrough the chamber according to the invention to interact with residuesbeing carried by the gases towards the gas outlet, as explained above.The upstream position of the gas outlet in relation to the melting zoneis thus also important in the context of the present invention. In theabsence of a column of waste, or where the gas outlet is not upstream ofthe hot zone, the gases carrying the residues are substantially freelyvented from the chamber, and cannot effectively interact with slag orother materials that are input to the processing chamber. Furthermore,the column of waste helps to maintain quasi steady state conditionswithin the processing plant, and a stable temperature profile is alsomaintained therein, comprising a relatively cooler upper zone, hereinthe gasification zone, and a lower hotter zone, herein the melting zone,close to the plume generated by the plasma torches of the processingchamber. In the upper gasification zone, organic material is gasified.In the lower melting zone inorganic materials are converted into moltenmetals and molten slag, which may be removed separately or together.When the residence time of the inorganic material in the melting zone issufficiently large, at least part of the slag (including oxides andother chemical elements) will be vitrified. On the other hand, when theresidence time is not sufficiently long to produce vitrification, themolten slag, when cooled, will form solidified fused slag. In thepresent invention, the melting zone provides conditions such that all ofthe inorganic material may eventually be melted, given sufficientresidence time, and typically also that at least a part of the inorganicmaterial will be converted into fused slag, when non-metallic inorganicmaterials are included in the waste. Preferably, all of the inorganicmaterial is converted into vitrified slag, and thus the melting zone mayalso be referred to as the vitrification zone.

As inorganic waste in the downstream part of the column is melted, andas organic waste in the upper part is gasified, the waste in the columngradually migrates towards the downstream end, and more waste may beinput into the chamber. This, however, does not substantially affect thequasi-steady state conditions in the chamber referred to above.

While the high temperature zone is preferably provided by at least oneplasma torch means, as will be described in greater detail herein, othermeans may also be used for providing this high temperature zone, so longas conditions are provided in the melting zone such as to meltsubstantially all of the inorganic material comprised in the wasteaccommodated therein. For example, preheated oxidizing gas such as airor oxygen, mixed with suitable fuel such as coke, for example, may beused to provide the melting zone. The temperature in the melting zonemay be further augmented in either case using an oxidizing fluid, withfuel, or air by itself that may be preheated to high temperatures, suchas 1000° C. or more using a regenerative heat exchanger associated withthe post-processing means (200), described herein.

Typically, a solid or mixed waste feeding system (20) introducestypically solid waste at the upper end of the chamber (10) via a wasteinlet means comprising an air lock arrangement (30). Mixed waste mayalso be fed into the chamber (10), though generally gaseous and liquidwaste is removed from the apparatus (10) without substantial treatment.The solid/mixed waste feeding system (20) may comprise any suitableconveyor means or the like, and may further comprise a shredder forbreaking up the waste into smaller pieces. The air lock arrangement (30)may comprise an upper valve (32) and a lower valve (34) defining aloading chamber (36) therebetween. The valves (32), (34) are preferablygate valves operated electrically, pneumatically or hydraulically toopen and close independently as required. A closeable hop arrangement(39) funnels typically solid and/or mixed waste from the feeding system(20) into the loading chamber (36) when the upper valve (32) is open,and the lower valve (34) is in the closed position. Feeding of wasteinto the loading chamber (36) typically continues until the level ofwaste in the loading chamber (36) reaches a predetermined point belowfull capacity, to minimise the possibility of any waste interfering withclosure of the upper valve (32). The upper valve (32) is then closed. Inthe closed position, each of the valves (32), (34) provides an air seal.When required, the lower valve (34) is then opened enabling the waste tobe fed into the processing chamber (10) with relatively little or no airbeing drawn therewith. The opening and closing of the valves (32), (34),and the feeding of waste from the feeder (20) may be controlled by anysuitable controller (150), which may comprise a human controller and/ora suitable computer control system, operatively connected thereto and toother components of the plant (100). Preferably, a waste flow sensingsystem (130) is provided and operatively connected to the controller(150). The sensing system (130) typically comprises one or more suitablesensors (33) at an upper part or level (F) of the chamber (10) forsensing when the level of waste reaches this level. Similarly, thesensing system (130) typically also comprises one or more suitablesensors (33) at a level (E), vertically displaced downwards with respectto level (F) of the chamber (10), for sensing when the level of wastereaches this level. Level (F) may advantageously represent the maximumsafety limit for waste in the chamber (10), while level (E) mayrepresent a level of waste within the chamber (10) at which it isefficient to provide more waste to the chamber (10). Thus, the volume inthe chamber (10) between level (E) and level (F) may be approximatelyequal to the volume of waste that may be accommodated in loading chamber(36). Alternatively, or additionally, the location of the sensors (33)and (33′) at levels (F) and (E) may be chosen to provide suitable datumsfor determining an actual flow rate of the waste through the chamber(10) by measuring the time interval between the time when the level ofwaste is at level (F) to when it reaches level (E), for example. Thecontroller (150) may also be operatively connected to valves (32), (34)to coordinate loading of the loading chamber (36) from the feedingsystem (20), and unloading of the waste from the loading chamber (36) tothe processing chamber (10).

Optionally, the hop arrangement (39) may comprise a disinfectantspraying system (31) for periodically or continuously spraying the samewith disinfectant, as required, particularly when medical waste is beingprocessed by plant (100).

The processing chamber (10) comprises a lower part (17), herein definedas comprising the hot melting zone of the chamber, wherein pyrolysis andvitrification of inorganic material into molten and preferably vitrifiedinorganic slag and into molten metal takes place. The lower part (17)comprises a liquid product collection zone (41), typically in the formof a crucible, having at least one outlet (65) associated with one ormore collection reservoirs (60). The processing chamber (10) furthercomprises at the upper end thereof at least one gas outlet (50),primarily for channeling product gases, generated from the processing ofwaste, away from the processing chamber (10). The upper end of theprocessing chamber (10) comprises the said air lock arrangement (30),and the processing chamber (10) is typically filled with waste materialvia the airlock arrangement (30) up to about the level of the primarygas outlet (50). Sensing system (130) senses when the level of wastedrops sufficiently (as a result of processing in the chamber (10)) andadvises controller (150) to enable another batch of waste to be fed tothe processing chamber (10) via the loading chamber (36). The controller(150) then closes lower valve (34) and opens upper valve (32) to enablethe loading chamber (36) to be re-loaded via feeding system (20), andthen closes upper valve (32), ready for the next cycle.

One or a plurality of plasma torches (40) at the lower part (17) of theprocessing chamber (10) are operatively connected to suitable electricpower, gas and water coolant sources (45), and the plasma torches (40)may be of the transfer or non-transfer types. The torches (40) aremounted in the chamber (10) by means of suitably sealed sleeves, whichfacilitates replacing or servicing of the torches (40). The torches (40)generate hot gases that are directed downwardly typically at an angleinto the bottom end of the column of waste. The torches (40) aredistributed at the bottom end of the chamber (10) such that inoperation, the plumes from the torches (40) heat the bottom of thecolumn of waste, as homogeneously as possible, to a high temperature,typically in the order of about 1600° C. or more. The torches (40)generate at their downstream output ends hot gas jets, or plasma plumes,having an average temperature of about 2000° C. to about 7000° C. Theheat emanating from the torches (40) ascends through the column ofwaste, and thus a temperature gradient is set up in the processingchamber (10). Hot gases generated by the plasma torches (40) support thetemperature level in the chamber (10). This temperature level issufficient at least at the lower part of the chamber (10) forcontinuously converting the waste into product gases that are channeledoff via outlet (50), and into a liquid material (38) that may includemolten metal and/or slag, which may be periodically or continuouslycollected at the lower end of the chamber (10) via one or more slagoutlets (61) and into one or more reservoirs (60). Typically, the moltenmetal and the slag are collected separately in dedicated reservoirs.Hereinafter, unless otherwise specified, the reference numeral (60)indicates the slag reservoir.

Oxidising fluid may be provided from a suitable source (70) to convertchar, produced during pyrolysis of organic waste, into useful gases suchas CO and H₂, for example. The oxidising fluid is introduced to thelower part of the chamber (10) via one or more suitable inlet ports(75). “Oxidising fluid” is herein taken to include any gas or otherfluid capable of oxidising at least in part char found or produced inthe hotter, lower parts of the processing chamber of the wasteprocessing apparatus, and includes oxygen, steam, air, CO₂ and anysuitable mixture thereof.

The inner facing surfaces of processing chamber (10), at least of thelower part thereof, are typically made from one or more suitablerefractory materials, such as for example alumina, alumina-silica,magnesite, chrome-magnesite, chamotte or firebrick. Typically, theprocessing chamber (10), and generally the plant (100) as a whole, iscovered by a metal layer or casing to improve mechanical integritythereof and to enable the processing chamber to be hermetically sealedwith respect to the external environment.

As described in more detail hereinbelow, the plant (100) furthercomprises post processing means (200) operatively connected to said gasoutlet (50) via gas line (101), wherein the gas products generated inthe chamber (10) are processed and cleaned, producing in the processnon-gaseous residues. In general, non-gaseous residues are produced bythe post-processing means (200), and these residues include one or bothof subcategories Residues 1 (R1) and Residues 2 (R2), as hereinbeforedescribed.

Alternatively, the plant (100), in particular the post-processing means(200), may further comprise an afterburner means (300) operativelyconnected to the outlet (50) via gas line (101) for burning organic orother combustible components in the product gases, without comprising ascrubber means. The post-processing means (200) typically furthercomprises a suitable energy block or afterburner energy utilisation orgenerating system (400) operatively connected to the afterburner means(300) downstream thereof. Such energy utilisation systems (400)according to the present invention may include, for example, a boilerand steam turbine arrangement or the like coupled to an electricgenerator. The energy generated by the afterburner energy utilisationsystem (400) may be used to power the plant (100) and/or be exported,for example. As described hereinbefore, Residues 1 (R1) is typicallyprecipitated from the afterburner means (300) and from the energyutilization means (400).

The post-processing means (200) further comprises a suitable gascleaning system (500) downstream of the energy utilisation system (400),which may produce solid waste materials, and/or liquid solutionscomprising waste materials, including Residues 2 (R2), which requirefurther processing.

For example, the gas cleaning system (500) may comprise a “dry” gascleaning system, and may thus include a semi-dry scrubber, into which isfed a suspension of Ca(OH)₂ in water for binding the acid gases. Wateris subsequently evaporated fully, and thus only gases, products Ca(OH)₂,CaCl₂, CaSO₄, Ca₃(PO₄)₂, in powder form, and other dust (which did notprecipitate in the boiler) exit the scrubber. After the scrubber thereis a reactor-adsorber arrangement, wherein a mixture of powders ofCa(OH)₂ and powdered activated carbon (PAC) are fed. These powderedadsorbants have very large specific surface values (typically carbon>750m²/g; Ca(OH)₂>30 m²/g), and the Ca(OH)₂ may adsorb the remaining acidgases, while the PAC adsorbs dioxins and components containing heavymetals. After the reactor-adsorber there is a fabric filter arrangementwhere Residues 2 (R2) are precipitated, including Ca(OH)₂, activecarbon, dioxins, some oxides and salts (which did not precipitatebefore), and products of reaction (CaCl₂, CaSO₄, Ca₃(PO₄)₂ and othersubstances). Essentially, gas carrying dust, which includes toxiccomponents such as dioxins, heavy metals and their oxides and salts, isfiltered through the layer of dust precipitated in the bags andincluding adsorbents such as for example Ca(OH)₂ and PAC, and the toxiccomponents are adsorbed and thus precipitate out of the carrier gas. Theclean gas obtained after filtration is directed to an exhauster and thento the stack for expulsion into the atmosphere. Residues 2 (R2) obtainedfrom such a cleaning system (in particular from the bag filterarrangement) do not include liquid, and thus such systems are known as“dry” cleaning systems. Residues 2 (R2) are very toxic and may includedioxins, compounds of heavy metals and Ca(OH)₂, active carbon, someoxides and salts (which did not precipitate previously), products ofreaction (such as, for example, CaCl₂, CaSO₄, Ca₃(PO₄)₂ and othersubstances). However, since this Residue 2 (R2) is hygroscopic(especially the CaCl₂ portion thereof), it may absorb water from thewater vapour that is generated along with other combustion products, andthus may have a sludge-type consistency. Accordingly, tubes which areused for transporting this Residue 2 (R2) in the gas cleaning system(500) may be optionally heated to enable the Residue 2 to dry.

The post-processing means (200) exemplified in these figures alsocomprises a suitable stack arrangement (600) for channeling gases fromthe gas cleaning system (500) to the atmosphere. The stack arrangement(600) comprises suitable monitoring equipment to monitor that the levelsof pollutants exhausted therefrom to the atmosphere are within legallyacceptable limits.

Thus, the post-processing means (200) generates Residues 1 (R1) andResidues 2 (R2), as described hereinbefore.

In each one of the first, second and third embodiments, the residuerecycling means (900) typically comprises one or more reservoirs (950)for temporary storage and accumulation of Residues 1 (R1) and Residues 2(R2) precipitated by the post-processing means (200), as illustratedschematically in FIGS. 4, 5 and 6, and also in FIGS. 7, 8 and 9.

Residues (R1) and (R2) are usually precipitated by gravity into separatereservoirs (950), which are designated reservoirs (250) and (550),respectively, in FIGS. 7, 8 and 9. The residues are typically dischargedcontinuously through chutes (251), (551), respectively, into conveyortroughs (not shown) comprised in the reservoirs (250) and (550),respectively. In each reservoir, the residue conveyor pulls the settledresidue from the bottom of the trough and transports it to an ashhopper, storage bin, roll-off carrier, or dump truck (not shown). Thetrough is constructed of steel or concrete, and the residue-dischargesystem usually has two conveyor troughs so that a full standby isavailable. Having a full standby permits switching between systems foreven wear and scheduled maintenance. Preferably, though, suitable augersystems or pumping systems may be used for transporting the residues outof the reservoirs, wherein a liquid medium is used for transportation;for example—spent oil or fuel. Alternatively, steam or compressed airmay be used as a transport medium for residue transportation in dustform.

The present invention is characterised in providing a residues recyclingsystem (900) for recycling non-gaseous residues, such as to ensuredirect processing thereof at the hotter parts of the processing chamber(10). Referring to FIG. 6, in the third and preferred embodiment of thepresent invention the residues recycling system (900) comprises both thedirect feed system (700) and the indirect feed system (800),substantially as each described herein with respect to the first andsecond embodiments, respectively, mutatis mutandis.

In the first embodiment of the present invention, and referring to FIG.7, the residues recycling system (900) is in the form of a direct feedsystem (700), configured to directly channel at least a part of theresidues precipitated in the gas processing means (200) to the hotterlower part (17) of the chamber (10). Similarly, and referring to FIG. 9,the residues recycling system (900) of the third embodiment alsocomprises a direct feed system (700). Typically, Residues 1 (R1) arefirst accumulated in the reservoir (250), which is in fluidcommunication with the hotter lower part (17) of the chamber (10) via asuitable conduit means (710) comprised in the direct feed system (700).Suitable fluid transport means (720) may be used for assisting in thetransportation of the residues (R1) from the reservoir (250) to thechamber (10), and may utilize a suitable fluid medium, which may be ingaseous form such as steam, oxygen or air, or in liquid form such asfuel, used oil, liquid waste and so on, as hereinbefore described. Sucha fluid medium provided at a suitable high pressure by the fluidtransport means (720), which is in fluid communication with thereservoir (250), mixes the residues within the fluid and transports theresidues mixture downstream directly to the chamber (10).

Additionally or alternatively, the direct feed system (700) comprisesmechanical transport means (730) for transporting the residues to thechamber (10). The mechanical transport means (730) may comprise, forexample, a suitable pump such as a screw auger to displace the residuesfrom the reservoir (250) to the lower end of the chamber (10). Asuitable fluid may be further provided to the residues, typically whilestill in the reservoir (250), via fluid reservoir (740) to facilitatethe operation of the mechanical transport means (730), which isstrategically operatively connected to the conduit means (710).

The conduit means (710) comprises one or more outlets (760) located atthe lower, hot part (17) of the chamber (10). In particular, the outlets(760) are preferably located a short distance above the plasma jetsgenerated by the plasma torches (40), or otherwise close enough to thejets such that the residues are introduced to as hot a part of chamber(10) as possible. For example, FIG. 10(a) illustrates a fragmented viewof a configuration of the chamber (10), wherein the plasma torch (40) ismounted at an angle with respect to a substantially vertical wall (15)thereof, which is made from a refractory material. The outlet (760) ofconduit means (710) is located in a plane above but close to the plasmatorch (40). In view of the high temperatures in the lower part of thechamber (10), the outlet (760) may comprise a cooling jacket arrangement(770). Alternatively, and as illustrated in FIG. 10(b), in someconfigurations of the plant (100), the plasma torches (40) may bevertically mounted in side chambers (18) comprised in chamber (10), andthe outlet (760) may also be located in the side chamber (18) close tothe plume end of the plasma torch (40). As in the embodiment of FIG.10(a), the outlet (760) may comprise a cooling jacket arrangement (770).

The residues recycling system (900) can also be used, perhaps in a morelimited fashion, for recycling Residues 2 (R2), typically produced inthe gas cleaning system (500). In all embodiments, the residuesrecycling system (900) thus preferably comprises a suitable reservoir(550), provided for the temporary storage and accumulation of Residues 2(R2) precipitated by the gas cleaning system (500), or more generallyoriginating from the post-processing means (200). The reservoir (550) istypically similar to the reservoir (250) as hereinbefore described withrespect to Residues 1 (1), mutatis mutandis.

Thus, referring to FIG. 7 and FIG. 9, in the first and third embodimentsof the present invention, the direct feed system (700) further comprisesa suitable conduit means (520), providing fluid communication betweenthe reservoir (550) and conduit (710), and also preferably comprisessuitable pumping means. In this manner, and via conduit (710), theResidues 2 (R2) can be introduced, together with Residues 1 (R1) fromreservoir (250), to the lower hotter part of the chamber (10).Alternatively, the conduit means (520) may instead be routed to thereservoir (250), to be mixed with Residues 1 (R1) before proceeding tothe conduit means (710). Alternatively, the direct feed system (700) maybe configured so as to enable Residues 2 (R2) to be directly introducedto the chamber (10) separate from the Residues 1 (R1), and for thispurpose the conduit (520) may be directly connected to the lower part ofthe chamber (10), in a similar manner to that described for the conduitmeans (710), mutatis mutandis. Thus, the direct feed system (700)preferably comprises suitable mechanical transport means (not shown) fortransporting the Residues 2 (R2) to the chamber (10), and suchmechanical transport means may comprise, for example, a suitable pumpsuch as a screw auger to displace the residues from the reservoir (550)to the lower part (17) of the chamber (10). Suitable valve means (560)are provided in the conduit means (520) to control and interrupt theflow of Residues 2 (R2) to the chamber (10) when required. Residues 2(R2) may be mixed with liquid organic waste, such as for example usedengine oil, or liquid fuel, and fed via said direct feed system (700) tothe lower part of chamber (10).

In the second embodiment of the present invention, and referring to FIG.8, the residues recycling system (900) is in the form of an indirectfeed system (800), configured to encapsulate the residues in a thermallyand mechanically protecting matrix of slag and other additives, and tothen channel the encapsulated residues to the chamber (10). Similarly,and referring to FIG. 9, the residues recycling system (900) of thethird embodiment also comprises an indirect feed system (800).Typically, the Residues 1 (R1) are first accumulated in the reservoir(250), after precipitation from the gas processing means (200). Theindirect feeding system (800) comprises a mixing chamber (820), which isin fluid communication with reservoir (250) via conduit (825). At leastpart of the residues accumulated in the reservoir (250) are fed to themixing chamber (820) via gravity or any suitable pumping arrangement(not shown), and the Residues 1 (R1) are mixed in the mixing chamber(820) with an encapsulating material, typically slag and optionallyother reagents. Thus the residues are typically mixed with reagents andslag, and encapsulated or glued to form pellets or granules in such amanner such as to prevent their being carried out by gas from the upperpart of chamber (10). Such granules make the residues stable not onlythermally but mechanically too, and thus affords them greater time toreach the hot zone in the lower part (17) of the chamber (10). Inaddition, the granules may also interact with different compounds in thechamber (10) as they migrate downwards towards the melting zone, andsome volatile materials may react with different compounds in thegranules or may form solid solutions. Alternatively, some components maydiffuse from the surface into the granules (even in solid form). Theterms “granules” and “pellets” are used herein interchangeably, andrefer to a mass of material comprising said residues and anencapsulating material, typically slag and/or suitable reagents, hereinreferred to as “additives”, which optionally include one or moreadhesive-type materials such as cement or glue, for example. Thus, theseadditives are characterized by having adhesive properties, that is, theybind together particles of the residues into a matrix, and further, thematrix thus formed does not disintegrate under the conditions found inthe upper part of the processing chamber, rather, the matrix isdestroyed at the elevated temperatures which are to be found in thelower hotter part of the processing chamber. Such adhesive additives mayinclude, for example any one or combination of cement, sodium silicate,organic compounds including thermoplastics, and inorganic compoundsand/or complexes including oxide powders, oxide solutions, salt powdersand salt solutions.

Thus the encapsulating material has the function of enabling theresidues to be at least partly embedded in it or encapsulated by it,such as to thermally and mechanically stabilize the residues for asufficient period correlated to the migration time from the upper end tothe lower, hotter end of the chamber (10), as will become clearerhereinbelow. Such encapsulating material, hereinafter referred to asadditives, may include, for example, cement optionally mixed with water,silica glass (also known as liquid glass or mNa₂O.nK₂O.fSiO₂, wherein m,n, f are numerical factors including integers and fractions), or liquidorganic waste (including machine oil, for example), or slag, or indeed amixture of any of these additives. These components may be provided tothe mixing chamber (820) via suitable silos or reservoirs (830), bymeans of conduits (835) and gravity feeds or suitable pumps (not shown).The slag may additionally or alternatively be provided directly from thechamber (10) via reservoir (60), after the slag has been cooled andbroken up into suitable sized particles via transportation means (840),which may include a conduit, conveyor arrangement, or vehiculartransport, among others.

Typically, slag may be cooled into granules (for example by pouring itout in water from the chamber (10)) and it may then be mixed withreagents and with residue. When slag is poured out into the water, thediameter of granules formed depends on the melt jet mass flow and thediameter of the jet (which depends on chamber's productivity) and may beless then 3 cm. Such a system may also include a rotating drum. Whenslag with water is poured out onto the drum granules of slag are ejectedto different distance depending on their diameter. Granules or particlesof slag may also be further crushed before introduction into the mixer(820) if required. Alternatively, the slag granules or particles may beformed by first pouring the molten slag into metal moulds. The mouldsmay be of a suitable size such that each mould provides a singlegranule. Alternatively, the mould may be much larger than the desiredgranule size, and once the slag has cooled and solidified, the granulesare formed by mechanically crushing and splitting the solidified slagingot to provide granules or particles of slag.

The residues are typically encapsulated or are glued to slag by suitableadditives. A screw auger system, for example, may take out the mixtureof residues and additives, which may be in sludge form, from the mixer(820) into a pellet making machine or granulating means (850), wherepellets or granules are subsequently dried by air jets, for example.Some of the residue particles will be encapsulated, while others may beat the surface of the pellets. In any case, they are mechanically boundin the pellets such as to prevent the residue particles in the pelletsto be removed from the chamber (10) by product gases. The pellets orgranules thus formed may comprise a simple mixture, which is notdisintegrated because of the adhesive agent used in forming the matrix.Alternatively, some of the reagents that exist in the mixer (820) mayreact with the slag and residue during the mixing and subsequentformation of the granules. For example cement (which includescomponents: CaO.mSiO₂; KCaO.nA1₂O₃; fCaO.A1₂O₃.Fe₂fO₃ and others) may beused, and may thus react with water and may form some compounds and/orcomplexes with components of residue, which may include the same oxides,resulting in a matrix where the metal oxides are bound and therefore notcapable of volatizing until the matrix structure is destroyed byexposure to the high temperature zone in the lower part of theprocessing chamber.

The volume (Vg) and external surface area (Fg) of the residue granulesprovided by the granulating means (850) may be advantageously controlleda n d optimized according to the following criteria, wherein preferably,the volume (Vg) and external surface area (Fg) of the residue granulesare chosen such that they satisfy the relationship:—Vg/Fg≧0.00002*Hwherein H is a predetermined linear distance that is preferably but notnecessarily correlated to the travel distance of the residue granulesfrom the upper part of the chamber (10) to the lower, hotter partthereof. Thus, H is advantageously and preferably defined in theseembodiments the height of the chamber (10), taken from the center of thegas outlet (50) to the centre of the slag outlet port (61), asexemplified in FIG. 7. Alternatively, H may be defined as the verticaldistance taken from the center of the gas outlet (50) to either thenominal or maximum level of the surface of the slag at the lower part(17) of the chamber (10) (marked as (H′) in FIG. 7, for example), oralternatively to the hot zone of the lower part (17) provided by theplasma torches (40) (marked as (H″″) in FIG. 7, for example), oralternatively to the center of the output end of one of the plasmatorches, preferably of the uppermost plasma torch (marked as (H′″) inFIG. 7, for example). or alternatively to the bottom end of the chamber(10) (marked as (H″) in FIG. 7, for example). According to the level ofporosity of the residue granules, these may also comprise acorresponding internal surface area.

Thus, the mixture of residues and additives is then fed from the mixingchamber (820) to granulating means (850), to form suitably sizedgranules or pellets. Thereafter, a suitable transportation system (855)carries the granules to the upper end of the chamber (10), via a wasteinlet means comprising an air lock arrangement (30), either via thewaste feeding system (20) or directly. (At this point, of course, thegranules may additionally or alternatively be stored at a suitablelocation for future use, and/or transported to a different plant (100)for recycling therein.) The granules are then introduced into thechamber (10) together with other waste from the feeding system (20), orwithout such waste, and then migrate downwards to the lower hotter part(17) of the chamber (10), as herein described. Thus, the encapsulationof the residues by the additives substantially prevents the residuesfrom prematurely being carried out of the chamber (10) relativelyintact, exiting thereof via outlet (50). Rather, some of theencapsulated residues interact with reagents during the downwardmigration, while other residues are enabled to reach the lower hotterpart of the chamber (10).

This embodiment has the added advantage that slag, which is also afluxing agent, may be continually added to the column of waste,minimizing the risk of congestion therein. Also, the granules provide acertain degree of “porosity” to the column of waste, which is helpful inmaintaining a good distribution of heat and temperature gradient in thechamber (10).

Thus, by enabling the recycled residues to be exposed to the hightemperature of the hot, lower part (17) of the chamber (10), some oxidescontained in the residues which have low melting temperatures may be“absorbed” by other melted material therein. Different oxides may formsolutions and new compounds having higher melting temperatures than someof the original components thereof. For example, materials such aspyroxene minerals may be formed, which may include oxides of Na, Ca, Mg,Fe, Al, Cr, Ti and Si in different proportions. Further, reagents (addedto the residues and/or the slag that is being recycled (see below)) mayform such compositions with slag and/or with the residues beingrecycled, to allow volatile components to be trapped. Such volatilecomponents may be formed, for example, from the recycling of residues orfrom the waste, and tends to ascend in the processing chamber in vapourform through the column of waste. In mineral muscovite,(KAl₂(OH)₂[AlSi₃O₁₀]), different elements may be replaced therein, forexample, K may be replaced with Na, Cs, Ca or Ba; Al may be replacedwith Fe, Li, Cr, Mn or V; OH may be replaced with F. Such compositionsmay trap different toxic components. In such a manner it is possible toinclude in the slag some heavy metals, such as Cd, Zn, Pb, for example,which were originally in the residues, and thus rendering the same safefor disposal.

Referring to FIG. 8 and FIG. 9, in the second and third embodiments ofthe present invention, a conduit means (570) and suitable pump means(not shown) enables Residues 2 (R2) to be introduced to the mixingchamber (820) from reservoir (550). In the mixing chamber (820),Residues 2 (R2) may be mixed with additives in a similar manner to thatdescribed for Residues 1 (R1), mutatis mutandis, optionally in additionto Residues 1 (R1) from reservoir (250). The conduit means (570) and theconduit (825) may each comprise suitable valves, (828) and (528)respectively, for controlling the flow of Residues 1 (R1) and Residues 2(R2), respectively, to the mixing chamber (820), thereby enabling therelative amounts of Residues 1 (R1) and Residues 2 (R2) introducedtherein to be controlled. Alternatively, the conduit means (570) mayinstead by routed to the reservoir (250), to be mixed with Residues 1(R1) before proceeding to the mixing chamber (820) or granulating means(850), and valve means (528) may then be used to control the amount orproportion of Residues 2 (R2) being introduced therein. Alternatively,the indirect feed system (800) may be configured so as to enableResidues 2 (R2) to be directly mixed with additives and then introducedto the chamber (10), separate from the Residues 1 (R1). For this purposethe conduit (570) may be directly connected to a separate mixingchamber, having additive reservoirs in communication therewith, and agranulating means, and a suitable transport means similar but separateto that described herein for the Residues 1 (R1), mutatis mutandis.

In any case, the indirect feed system (800) provides granules that maybe fed into the chamber (10) via the upper end, in the same manner as,and typically together with, regular waste. As the granules descendthrough the increasing temperature zones of the chamber (10), they arecorrespondingly heated. However, the temperature inside each granule isdifferent from that at its surface. The larger the granule the greaterthe temperature difference between center and surface of the granule.Similarly, the lower the thermal conductivity of the granule materialthe greater the temperature difference between center and surface of thegranule. Also, for a given material, the greater the porosity thereof,the lower its effective thermal conductivity.

For example, it is known that for a material having the thermalproperties of wood (with known humidity), the time (t) in hours requiredfor the center temperature of a sphere (radius (r) in inches) of thematerial to reach the surface temperature can be given by the followingapproximate equation for a particular external temperature and physicalcharacteristics of the pellet [Hazardous Waste and Solid Waste. Editedby David H. F. Liu, Bela G. Liptak. 2000. Lewis Publishers]:t≈0.5*r ²

Thus, this equation indicates that for a wood-like material about onehour is needed for the center of a 3-in diameter pellet to approach thesurface temperature. Similar relationships between (t) and (r) may alsobe derived theoretically and/or empirically for other materials.

Thus, if the granules provided by the indirect feed system (800) aresufficiently large and also have low thermal conductivity (aided in thisrespect if the granules are also porous) some of the toxic components inthe residues may exist relatively intact within the granules while thesedescend to the hotter parts of the chamber (10). At the same time,relatively small particles of inorganic materials (which may exist inthe waste, or alternatively may be added to the waste for the purpose ofaiding recycling of residues) may melt at the same level of the chamber(10) as the aforesaid granules. Thus, when volatile components arereleased from the inside part of the large granules they are able tomake contact with the hot surface of the granules or with inorganicparticles in the molten state, or even with hot or melted material ofthe same large granules at their surface, and thus the volatilematerials may be subsequently absorbed and/or adsorbed, and may reactwith the material in contact therewith. Thus, the actual granule sizeand composition may be important parameters for the efficient recyclingof residues, and these parameters may be optimized for each type ofchamber (10), typically depending on the residence time of the granulesinside the chamber (10). Accordingly, it is advantageous to produceporous granules, and to control the composition and structure of thegranules such as to provide at the surface of the granules suchcomposition which may itself trap volatile toxic components.

In each of the three exemplified embodiments, some quantities ofResidues 2 (R2) may be accumulated in the gas cleaning system and cannot be treated there or indefinitely recycled. This may lead toexceeding the legally acceptable levels of toxic components in the stack(600), and these residues (R2) may be placed in special storage untilthe composition of the waste being input to the chamber (10) is“cleaner”, i.e., with less heavy metals, chlorine and sulphur and so on.

Residues 2 (R2) typically contain Ca(OH)₂, CaCl₂, CaSO₄, CaCO₃, NaOH,NaCl, Na₂SO₄, metal oxides, hydroxides and/or sulphides from many metalsincluding heavy metals, dioxins and other materials which are normallyinappropriate to be disposed of in land fills. The volume of residue ofthese materials may be significantly reduced using the system of thepresent invention by recycling Residues 2 back into the hotter parts ofthe chamber (10) as described above. Ordinarily, these materials reactat relatively low temperatures, say about 200° C., such as those foundin the upper part of the chamber (10), to produce HCl and other productswhich are not desirable.

However, when introduced to the hotter part of the chamber (10) as inthe present invention, these materials dissociate to the componentelements, and many of the metals may become embedded in the vitrifiedslag, typically as a solid solution, and thus rendered safe fordisposal. Different materials may be included in glasses (such asvitrified slag) in various proportions. For example, such glass mayinclude: Hg (<0.1%); S, C1, As, Se (<1% or more for special glasses) andoxides of metals: Cr, Ni, Mn, Co, Mo (3-5%); Ti, Cu, F, La, Ce, Cd, Th,Bi, Zr (5-15%); Li, B, Na, Mg, K, Ca, Fe, Zn, Rb, Cs, Sr, Ba, U(15-25%); A1, Si, P, Pb (>25%).

Thus, volatile components such as Cd, Zn, Cl, S, Hg, Pb, among others,contained in Residues 2, may be at least in some measure included in theslag, and thus removed from the eventual residue produced by the plant(100), by providing the Residues 2 directly to the hotter lower part(17) of the chamber (10). The amounts of these metals that can beeffectively removed from Residues 2 via the slag, will thus depend onthe possibility of the corresponding chemical element to be included inthe slag composition, and the relative amounts of slag produced by theplant (100). Thus, there is a limit on how much of these metals can beremoved from Residues 2, and therefore, at times the introduction ofResidues 2 to the chamber (10) may be slowed down or altogether stopped,to prevent these metals being endlessly recycled within the plant (100).

Further, and unlike Residues 1 (R1), Residues 2 (R2) cannot in normalcircumstances be fully recycled. The main reason is that compounds suchas CaSO₄ and Na₂SO₄ again form sulphur oxides in the high temperaturezone of the chamber (10), these oxides simply being converted in the gascleaning system (500) back to CaSO₄ and Na₂SO₄. Thus, these componentsof Residues 2 (R2) are not effectively removed by the recycling process,and must be disposed of by different means, for example via thetransport means (590). Thus, again, at times the introduction ofResidues 2 (R2) to the chamber (10) may be slowed down or altogetherstopped, to prevent these materials being endlessly recycled within theplant (100).

As mentioned hereinbefore, Residues 2 (R2) may also contain dioxins,particularly if the original waste processed by the chamber (10)contains PVC. The dioxins are hazardous materials which normally need tobe disposed of in a special way, with associated high costs for doingso.

In the present invention, one of the products of treating the residues,including dioxins, is HCl, which is mainly intercepted by the gascleaning system, but part of which is typically allowed to exhaust tothe atmosphere via stack (600). However, there are legal and safetylimits to such, and other, emissions, which must be monitoredcontinuously. For example, according to many international standards,for example as defined by the EU and by Germany, the limit (averagemaximum values in 24 hours, dry basis, 11% O₂) for HCl emissions is 10mg per cubic meter, and for SO₂ it is 50 mg per cubic meter. The levelof HCl (and other pollutants) may be measured at the stack (600) bysuitable sensors (650), and these parameters can be used as controlparameters for determining the appropriate feed rate of Residues 2 (R2)to the chamber (10). For example, if the level of HCl measured bysensors (650) exceeds a certain predetermined threshold, this could beindicative of too much Residues 2 (R2) being processed in the chamber(10), and thus the recycling rate of flow of Residues 2 (R2) may bereduced or stopped altogether, until the level of HCl and/or SO₂ (orother toxic components) is once again within acceptable limits. Ofcourse, if the level of chlorine and/or sulphur (or other elements thatform toxic compounds) still doesn't fall, this could mean that the wastebeing introduced via feed (20) contains high levels of HCl, and adifferent correcting action is needed.

In order to control the flow rate of Residues 2 (R2), the valve means(560) (in the first and third embodiments), and the valve means (528)(in the second and third embodiments), are advantageously operativelyconnected to a suitable controller, such as said controller (150). Saidcontroller (150) is also preferably operatively connected to the sensors(650), as well as other components of the chamber (10) as hereinbeforedescribed.

One of the main advantages—and indeed aims—of the present invention isto introduce into the vitrified slag, by means of recycling of residues,the components including the following heavy metals (Cd, Zn, Pb, Cu, Tl,Hg, Sb, As, Cr, Mn, Ni, V, and other), non-metals Cl, S, P, F (indifferent compounds). These chemical elements may be found in differentcomponents within the residues, depending on the specific technologicalarrangement of the plant (1), for example as illustrated in FIGS. 2(a),2(b), 3(a) or 3(b). Some of these components have low boiling points orare destroyed chemically at low temperatures (for example, Hg 356.7° C.,HgC1₂ 301.8° C., AsC1₃ 130° C.; HgO 400° C. destroyed, Cd(OH)₂ 300° C.destroyed). Other components have higher boiling points or arechemically destroyed at higher temperatures (for example, As 615-° C.,As₄S₄ 534° C., Pb 1745° C., PbC1₂ 953° C. PbS 1114° C., PbO 1516° C.,NiC1₂ 970° C., CuO 1026° C. (destruction temperature), ZnC1₂, 732° C.,Zn 906° C., Cd 766.5° C., CdC1₂ 964° C., CdO 900° C.). In the second andthird embodiments, the slag is provided by means of the granules orpellets that are introduced into the chamber (10).

However, and optionally, the system (900) according to any one of thefirst, second or third embodiments of the present invention may furthercomprise a slag recycling system (990) for directly recycling at leastpart of the slag formed by the plant (100), and possibly additives aswell, into the chamber (10). The slag recycling system comprises asuitable granulating or other converting means for converting at leastpart of said slag into slag particles, and means for transporting atleast a part of said slag particles to a suitable inlet comprised in thecooler part of said at least one processing chamber.

The recycling of slag helps in providing better heating distributionwithin the chamber (10), and also for trapping volatile components inthe waste itself and/or the recycled residues. When large amounts ofslag are produced by the chamber (10), part of the slag may be recycled,while the remaining slag may be sold to customers (63). Thus, andreferring to FIGS. 4 and 7, 5 and 8, and 6 and 9, the slag recyclingsystem (990) for the first, second and third embodiments, respectively,comprises a suitable conduit (995) operatively connected to thereservoir (60) and adapted for transporting at least part of the slagfrom the reservoir (60), granulated or otherwise converted to particlesof a suitable size, to the top of the chamber (10), in a similar mannerto the granules produced and transported by the indirect feed system(800) of the second and third embodiments, as described hereinbefore,mutatis mutandis. Optionally, the slag recycling system (990) mayfurther comprise a mixing chamber (996) operatively connected to theconduit (995) and reservoir (60), wherein additives may be added from anexternal source (997), to be mixed with the slag and the subsequentmixture granulated as before. Optionally, the slag recycling system maybe controlled via control (150).

The volume (Vr) and surface area (Fr) of the slag granules or particlesrecycled by the slag recycling system (990) may be advantageouslycontrolled according to the following criteria, in which preferably, thevolume (Vr) and surface area (Fr) of the slag granules or particles arechosen such that they satisfy the relationship:—Vr/Fr<Vg/Fgwherein (Vg) is the volume and (Fg) is the surface area of the granulesor particles produced by the indirect recycling system (800). The slaggranules or particles may optionally be provided from other wasteprocessing plants.

While the residues recycling system according to the present inventionis best incorporated as an integral part of a plasma-type wasteconverting or processing apparatus, the residues recycling system of thepresent invention is also retrofittable on many existing plasma-basedwaste processing apparatuses, according to individual circumstances.

While the residues recycling system according to the present inventionhas been described in the context of a plasma-torch based wasteprocessing plant and is particularly adapted therefor, the residuesrecycling system is also directed to any other type of waste processingplants which comprise at least one gas outlet means and also a hightemperature generating means adapted for providing a high temperaturezone in a lower part of said chamber at least sufficient for enablinginorganic waste accommodated therein to be converted into molten slag.Thus, the present invention is also applicable to non-plasma torch basedwaste processing plants. Such plants may include, for example,processing plants in which waste, such as municipal sewage waste, pluscoke or coal is supplied to the processing chamber via a top endthereof, and oxygen is provided via a lower end of the chamber,providing intense heat sufficient for the conversion of inorganic wasteto molten slag. Another example includes the type of processing plant inwhich MSW is fed to the processing chamber via an upper end thereof, andhot air, preheated oxygen and fuel gases are provided via a lower end ofthe chamber, providing intense heat sufficient for the conversion ofinorganic waste to molten slag. In these plants, product and wastegases, including residues, exit the processing chamber via one or moregas outlets.

While in the foregoing description describes in detail only a fewspecific embodiments of the invention, it will be understood by thoseskilled in the art that the invention is not limited thereto and thatother variations in form and details may be possible without departingfrom the scope and spirit of the invention herein disclosed.

1-60. (canceled)
 61. A residues recycling system for recycling at leastpart of the residues formed in a waste processing plant, said wasteprocessing plant having:— at least one waste processing chamber adaptedfor accommodating a column of waste and for enabling said waste tomigrate through the chamber in a downstream direction, said chamberhaving at least one upstream gas outlet means and further having hightemperature generating means adapted for providing a high temperaturemelting zone in a downstream part of said chamber and a relativelycooler upstream gasification zone, wherein said melting zone is atconditions at least sufficient for enabling substantially all inorganicwaste therein to be melted into at least one of melted metals conditionssufficient for enabling gasification of organic waste in said column ofwaste; at least one post processing means operatively connected to saidat least one waste processing chamber, wherein said post-processingmeans are adapted for enabling said residues to be collected therefromduring operation of said at least one waste processing chamber; whereinsaid residues recycling system is characterized in being adapted forintroducing at least a portion of said residues into the lower part ofsaid processing chamber such that during operation of said system saidportion of said residues is directly exposed to said high temperaturemelting zone provided by said high temperature generating means.
 62. Aresidues recycling system as claimed in claim 61, wherein said recyclingsystem comprises at least one collection reservoir operatively connectedto said post processing means and adapted for collecting at least partof the residues therefrom.
 63. A residues recycling system as claimed inclaim 61, wherein said residues comprise at least two types of residues,including residues 1 and residues 2 which differ one from the other inat least their chemical properties, that are separately collectible fromsaid post processing means, and said system comprises at least one saidcollection reservoir for separately collecting one or another of saidresidues 1 and residues
 2. 64. A residues recycling system as claimed inclaim 62, wherein said recycling system comprises suitable conduit meansfor providing communication between said at least one collectionreservoir and said lower part of said at least one processing chamber,said conduit means adapted for transporting said residues from said atleast one collection reservoir to said lower part of said at least oneprocessing chamber for direct exposure of said residues to said hot zoneduring operation of said system.
 65. A residues recycling system asclaimed in claim 64, wherein said system further comprises suitabletransport means operatively connected to said at least one collectionreservoir for assisting transportation of said residues through saidconduit means.
 66. A residues recycling system as claimed in claim 65,wherein said transport means comprises a suitable fluid medium fortransporting the said residues.
 67. A residues recycling system asclaimed in claim 63, wherein said system further comprises suitablemechanical transport means operatively connected to said at least onecollection reservoir for assisting transportation of said residuesthrough said conduit means.
 68. A residues recycling system as claimedin claim 67, wherein said transport means comprises a suitable pump fortransporting the said residues.
 69. A residues recycling system asclaimed in claim 63, wherein said conduit means comprises at least onesuitable outlet operatively connected to said lower part of saidprocessing chamber.
 70. A residues recycling system as claimed in claim63, wherein said conduit means comprises at least one suitable valveoperable to enable the flow of at least a portion of said residuesthrough said conduit means to be selectively prevented or allowed.
 71. Aresidues recycling system as claimed in claim 70, wherein said valve isoperatively connected to a suitable control system.
 72. A residuesrecycling system as claimed in claim 71, wherein said control system isfurther operatively connected to at least one suitable sensor comprisedin said post processing means and adapted for controlling the operationof said valve according to predetermined conditions sensed by saidsensor.
 73. A residues recycling system as claimed in claim 61, whereinsaid recycling system comprises a source of suitable additives and asuitable mixer for mixing at least a portion of said residues with saidadditives, said additives adapted for at least partially encapsulatingsaid portion of residues in a matrix that is thermally and mechanicallystable at temperatures substantially similar to the temperature of thegasification zone of said processing chamber, first granulating meansfor granulating said matrix into residue granules, and means fortransporting said residue granules to a suitable inlet comprised in apart of said at least one processing chamber that is cooler than themelting zone thereof.
 74. A residues recycling system as claimed inclaim 73, wherein said additives may be chosen from any one orcombination of cement, sodium silicate, organic compounds includingthermoplastics, and inorganic compounds and/or complexes including oxidepowders, oxide solutions, salt powders and salt solutions.
 75. Aresidues recycling system as claimed in claim 73, wherein said inlet isa waste inlet for enabling waste to be input into said at least oneprocessing chamber.
 76. A residues recycling system as claimed in claim73, wherein said additives comprise at least part of said slag, andfurther comprising means for introducing at least part of said slag intosaid mixer.
 77. A residues recycling system as claimed in claim 76,further comprising suitable transport means for transporting slagproduced by said at least one processing chamber to said mixer.
 78. Aresidues recycling system as claimed in claim 73, wherein said systemfurther comprises suitable transport means operatively connected to saidat least one collection reservoir for assisting transportation of saidresidues.
 79. A residues recycling system as claimed in claim 78,wherein said transport means comprises a suitable fluid medium fortransporting the said residues at least to said mixer.
 80. A residuesrecycling system as claimed in claim 73, wherein said system furthercomprises suitable mechanical transport means operatively connected tosaid at least one collection reservoir for assisting transportation ofsaid residues at least to said mixer.
 81. A residues recycling system asclaimed in claim 80, wherein said transport means comprises a suitablepump for transporting the said residues.
 82. A residues recycling systemas claimed in claim 73, further comprising at least one suitable valveoperable to enable the flow of at least a portion of said residues tosaid mixer to be selectively prevented or allowed.
 83. A residuesrecycling system as claimed in claim 82, wherein said valve isoperatively connected to a suitable control system.
 84. A residuesrecycling system as claimed in claim 83, wherein said control system isfurther operatively connected to at least one suitable sensor comprisedin said post processing means and adapted for controlling the operationof said valve according to predetermined conditions sensed by saidsensor.
 85. A residues recycling system as claimed in claim 73, whereinthe volume (Vg) and external surface area (Fg) of at least a portion ofsaid residue granules are chosen such that:Vg/Fg≧0.00002*H wherein H is a predetermined linear distance that iscorrelated to the travel distance of the residue granules from the upperpart of the processing chamber to the lower part thereof.
 86. A residuesrecycling system as claimed in claim 85, wherein H comprises the heightof the said processing chamber taken from the center of the said gasoutlet to the centre of a slag outlet port comprised in said lower partand adapted for enabling the molten slag to exit the said processingchamber.
 87. A residues recycling system as claimed in claim 85, whereinH comprises the vertical distance taken from the center of the said gasoutlet to a nominal level of the surface of the molten slag at the saidlower part of the said chamber
 88. A residues recycling system asclaimed in claim 85, wherein H comprises the vertical distance takenfrom the center of the said gas outlet to said high temperature zone ofsaid lower part of said processing chamber.
 89. A residues recyclingsystem as claimed in claim 85, wherein said processing chamber comprisesat least one plasma torch means and H comprises the vertical distancetaken from the center of the said gas outlet to the center of the outputend of said at least one plasma torches means.
 90. A residues recyclingsystem as claimed in claim 61, wherein said high temperature generatingmeans comprises at least one plasma torch means comprising an output endextending into a downstream part of said waste processing chamber saidat least one plasma torch means adapted for providing a high temperaturemelting zone in a downstream part of said chamber at least sufficientfor enabling substantially all inorganic waste accommodated therein tobe melted.
 91. A residues recycling system as claimed in claim 61,further comprising a slag recycling system for at least part of the slagformed in a waste processing plant and subsequently cooled andsolidified after extraction therefrom, wherein said slag recyclingsystem comprises a suitable converting means for converting at leastpart of said solidified slag into slag particles, and means fortransporting at least a part of said slag particles to a suitable inletcomprised in the cooler part of said at least one processing chamber.92. A residues recycling system as claimed in claim 91, wherein saidinlet is a waste inlet for enabling waste to be input into said at leastone processing chamber.
 93. A residues recycling system as claimed inclaim 91, further comprising means for introducing suitable additivesinto said converting means.
 94. A residues recycling system as claimedin claim 91, wherein the volume (Vr) and surface area (Fr) of at least aportion of said slag particles are chosen such that:Vr/Fr<Vg/Fg wherein (Vg) is the volume and (Fg) is the external surfacearea of the residue granules provided by said recycling system.
 95. Aresidues recycling system as claimed in claim 61, wherein at least aportion of said slag may be removed from said chamber and subsequentlycooled to provide solidified fused slag.
 96. A residues recycling systemas claimed in claim 61, wherein said conditions in said melting zoneprovided by said high temperature generating means are sufficient suchthat said melting zone is also a vitrification zone.
 97. A residuesrecycling system as claimed in claim 96, wherein at least a portion ofsaid slag may be removed from said chamber and subsequently cooled toprovide solidified vitrified slag.
 98. A waste processing plantcomprising:— at least one waste processing chamber adapted foraccommodating a column of waste and for enabling said waste to migratethrough the chamber in a downstream direction, said chamber having atleast one upstream gas outlet means and further having high temperaturegenerating means adapted for providing a high temperature melting zonein a downstream part of said chamber and a relatively cooler upstreamgasification zone, wherein said melting zone is at conditions at leastsufficient for enabling substantially all inorganic waste therein to bemelted into at least one of melted metals and slag, and wherein saidupstream gasification zone is at conditions sufficient for enablinggasification of organic waste in said column of waste; at least one postprocessing means operatively connected to said at least one wasteprocessing chamber, wherein said post-processing means are adapted forenabling said residues to be collected therefrom during operation ofsaid at least one waste processing chamber; and characterized in furthercomprising a residues recycling system as defined in claim
 61. 99. Awaste processing plant as claimed in claim 98, wherein saidpost-processing means comprises a suitable afterburner, a suitableenergy utilization means, a suitable gas cleaning system and a suitablestack operatively connected in series to said processing chamber.
 100. Awaste processing plant as claimed in claim 98, wherein saidpost-processing means comprises a suitable afterburner, a combustionproducts cooling system, a suitable gas cleaning system and a suitablestack operatively connected in series to said processing chamber.
 101. Awaste processing plant as claimed in claim 98, wherein saidpost-processing means comprises a suitable gas cleaning system, asuitable energy utilization means and a suitable stack operativelyconnected in series to said processing chamber, and further comprises awaste water treatment system operatively connected to said gas cleaningsystem.
 102. A waste processing plant as claimed in claim 98, whereinsaid post-processing means comprises a suitable gas cleaning system anda waste water treatment system operatively connected to said gascleaning system, and wherein said gas cleaning system is adapted forchanneling clean fuel gases therefrom to an external user.
 103. A wasteprocessing plant claimed in claim 98, wherein said high temperaturegenerating means comprises at least one plasma torch means comprising anoutput end extending into a lower part of said waste processing chambersaid at least one plasma torch means adapted for providing a hightemperature melting zone in a lower part of said chamber at leastsufficient for enabling substantially all inorganic waste accommodatedtherein to be converted into at least one of molten metal and slag. 104.A method for recycling at least a part of residues formed in a wasteprocessing plant, said waste processing plant having:— at least onewaste processing chamber adapted for accommodating a column of waste andfor enabling said waste to migrate through the chamber in a downstreamdirection, said chamber having at least one upstream gas outlet meansand further having high temperature generating means adapted forproviding a high temperature melting zone in a downstream part of saidchamber and a relatively cooler upstream gasification zone, wherein saidmelting zone is at conditions at least sufficient for enablingsubstantially all inorganic waste therein to be melted into at least oneof melted metals and slag, and wherein said upstream gasification zoneis at conditions sufficient for enabling gasification of organic wastein said column of waste; at least one post processing means operativelyconnected to said waste processing chamber, wherein said post-processingmeans are adapted for enabling said residues to be collected therefromduring operation of said at least one waste processing chamber; whereinsaid method comprises the steps: (a) collecting at least part of saidresidues from a said post processing means; and (b) introducing at leastpart of said residues into a said processing chamber such that duringoperation of said system said residues are exposed to said hightemperature melting zone provided by the said high temperaturegenerating means.
 105. A method as claimed in claim 104, wherein in step(a), said residues are collected in at least one suitable collectionreservoir operatively connected to said post processing means.
 106. Amethod as claimed in claim 105, wherein said residues comprise at leasttwo types of residues, including residues 1 and residues 2 which differone from the other by at least their chemical properties, that areseparately collectible from said post processing means, and wherein instep (a) residues 1 and residues 2 are separately collected in differentsaid collection reservoirs.
 107. A method as claimed in claim 105,wherein in step (b), said residues are transported from said at leastone collection reservoir to a lower part of said at least one processingchamber for direct exposure of said residues to said hot melting zoneduring operation of said system.
 108. A method as claimed in claim 105,wherein in step (b), suitable additives are mixed with at least aportion of said residues, said additives being adapted for at leastpartially encapsulating said portion of residues in a matrix that isthermally and mechanically stable at temperatures substantially lowerthat the temperature of said hot melting zone, said matrix is granulatedinto suitable residue granules, and said residue granules aretransported to a suitable inlet comprised in the cooler part of said atleast one processing chamber for introduction into the said at least oneprocessing chamber.
 109. A method as claimed in claim 108, wherein thevolume (Vg) and external surface area (Fg) of at least a portion of saidresidue granules are chosen such that:Vg/Fg≧0.00002*H wherein H is predetermined linear distance that iscorrelated to the travel distance of the residue granules from the upperpart of the processing chamber to the lower part thereof.
 110. A methodas claimed in claim 109, wherein H comprises the height of the saidprocessing chamber taken from the center of the said gas outlet to thecentre of the slag outlet port comprised in said lower part and adaptedfor enabling the molten slag to exit the said processing chamber.
 111. Amethod as claimed in claim 109, wherein H comprises the verticaldistance taken from the center of the said gas outlet to a nominal levelof the surface of the molten slag at the said lower part of the saidchamber
 112. A method as claimed in claim 109, wherein H comprises thevertical distance taken from the center of the said gas outlet to saidhigh temperature zone of said lower part of said processing chamber.113. A method as claimed in claim 109, wherein said processing chambercomprises at least one plasma torch means and H comprises the verticaldistance taken from the center of the said gas outlet to the center ofthe output end of said at least one plasma torches means.
 114. A methodas claimed in claim 104, further comprising the step (c) of introducingslag granules to a suitable inlet comprised in the cooler part of saidat least one processing chamber for introduction into the said at leastone processing chamber, said slag granules being produced by granulatingat least a portion of the slag provided by the said processing chamberduring operation thereof.
 115. A method as claimed in claim 114, whereinthe volume (Vr) and surface area (Fr) of at least a portion of said slaggranules are chosen such that:Vr/Fr<Vg/Fg wherein (Vg) is the volume and (Fg) is the external surfacearea of the residue granules provided in step (b).
 116. A method asclaimed in claim 114, wherein components of said residues are introducedinto slag, which is subsequently removed from said apparatus andsubsequently cooled and solidified to trap therein said components. 117.A method as claimed in claim 116, wherein said components include anyone or more of Cd, Zn, Pb, Cu, Tl, Hg, Sb, As, Cr, Mn, Ni, V, Cl, S, P,F, in elemental form or in compounds.
 118. A method as claimed in claim116, wherein conditions in said hot melting zone are such that the saidslag is vitrified thereat.
 119. A method as claimed in claim 114,wherein components of said residues form solid solutions with said slag,which is subsequently removed from said apparatus and subsequentlycooled and solidified to form vitrified slag.
 120. A method as claimedin claim 119, wherein said components include one or more of Hg, S, C1,As, Se and oxides of metals: Cr, Ni, Mn, Co, Mo (3-5%); Ti, Cu, F, La,Ce, Cd, Th, Bi, Zr (5-15%); Li, B, Na, Mg, K, Ca, Fe, Zn, Rb, Cs, Sr,Ba, U; A1, Si, P, Pb.